Also in 605, when Khitan tribes attack Ying Province (roughly modern Zhaotun, Liaoning), Emperor Yang has the official Wei Yunqi requisition Tujue troops under Ashina Rangan to attack the Khitan.

The Khitan forces are caught by surprise and defeated.

Ashina Rangan visits Emperor Yang at Luoyang in spring 607.

At the instigation of Yuwen Shu Emperor Yang has Yang Yong's eight sons put to death around the same time.

Emperor Yang abolishes provinces in summer 607 and changes them to prefectures.

At the same time, he reorganizes his father's governmental system of having five main bureaus, keeping four of the main bureaus—the executive bureau (Shangshu Sheng), the examination bureau (Menxia Sheng), the legislative bureau (Neishi Sheng), the archival bureau (Mishu Sheng)—while abolishing the eunuch bureau and replacing it with the palace bureau (Diannei Sheng).

He establishes three additional independent agencies and five independent departments.

He also organized the imperial army into sixteen corps.

He abolishes three levels of noble titles—the counts, the viscounts, and the barons—keeping only the princes, the dukes, and the marquesses.

Also in summer 607, Emperor Yang embarks on a tour of the northern provinces, building an imperial highway from Chang'an to …

…Jinyang (the capital of Bing Province).

He then personally visits the imperial tent of Ashina Rangan, whose display of submission and loyalty causes Emperor Yang to bestow much honor and wealth on him.

When the senior officials Gao Jiong, Yuwen Bi, and Heruo Bi privately express disapproval, Emperor Yang discovers their criticism and puts all of them to death, while removing Su Wei, who had also discouraged him from giving excessive rewards to Ashina Rangan, from his post. (Traditional historians attribute Gao's death to Gao's refusal to keep Chen Shubao's Consort Zhang alive in 589.)

As Xiao Cong has a deep friendship with Heruo Bi, and there have been rumors that the Xiaos will rise again, the superstitious Emperor Yang also removes Xiao Cong from his post.

Also in 607, at the instigation of Pei Ju, Emperor Yang reopens relations with the Western Regions, or Xiyu states.

Emperor Yang conscripts over a million men in spring 608 to construct the Yongji Canal, from the Yellow River to Zhuo Prefecture (roughly modern Beijing).

It is said that there were not enough men, and that he started conscripting women as well.

The Western Tujue khan (Ashina Rangan's western rival), the Heshana Khan Ashina Daman, whose mother was Han, submits to Sui as a vassal in 608 after persuasion by the Sui official Cui Junsu However, in the same year Emperor Yang receives a letter claiming to be from the King of Japan, Duolisibigu (now commonly believed to be Prince Shōtoku), stating, "The Son of Heaven where the sun rises, to the Son of Heaven where the son sets, may good health be with you."

Displeased by what he sees as insolence, he orders that in the future, "insolent" letters from other states not be submitted to him.

Also in 608, Emperor Yang's relationship with Yang Jian begins to deteriorate, initially over disputes over women (Yang Jian's having taken a concubine that Emperor Yang himself wanted) and hunting (Yang Jian's guards having been much more successful than Emperor Yang's guards at hunting).

He ordered investigations into Yang Jian's violation of laws, and discovers that Yang Jian had used witchcraft to curse Yang Zhao's three sons.

In anger, Emperor Yang executes and exiles a number of Yang Jian's associates, but he does not depose Yang Jian, although from this point on Yang Jian does not exert much influence on the political scene.

Ashina Rangan makes another visit to Emperor Yang in spring 609, and the emperor again rewards him with much treasure.

At the same time, Emperor Yang orders the redistribution of the farming land throughout the empire.

Also in 609, Emperor Yang, jealous of the literary talent of the official Xue Daoheng, falsely accuses Xue of defaming the emperor and has him strangled.

By this time, it is said that Emperor Yang's lifestyle has become particularly wasteful, and that he no longer feels bound by moral principles.

The emperor conducts a tour of the newly conquered Tuyuhun territory later in the spring, and sends several generals to chase down Murong Fuyun.

The Sui forces engage Murong Fuyun's remaining forces, with mixed success, but Murong Fuyun is forced to flee to Dangxiang tribes.

Emperor Yang tries to impose Murong Fuyun's son Murong Shun, whom Murong Fuyun had earlier sent to Sui as a hostage, as Tuyuhun's new khan, but the Tuyuhun people will not accept him, and Murong Shun is forced back to Sui territory.

Emperor Yang also receives twenty-seven rulers of Xiyu (Western Regions) kingdoms in an audience at Zhangye (in modern Zhangye, Gansu).

Ashina Rangan, khagan of the Easturn Turks, dies in late 609 and is succeeded by his son Shibi Khan Ashina Duojishi.

Pursuant to Tujue customs, Ashina Duojishi requests permission from Emperor Yang of Sui to marry Ashina Rangan's wife Princess Yicheng (the daughter of a clansman of Emperor Yang).

Emperor Yang agrees.