Sun Quan, in coordination with Zhuge Liang's final northern expedition against Wei, personally leads a major attack against Wei's border city Hefei in 234, while having Lu Xun and Zhuge Jin attack Xiangyang, with the strategy of trying to attract Wei relief forces and then attacking them.

However, Wei generals correctly see the situation and simply let Sun Quan besiege Hefei.

Only after Sun Quan's food supplies run low does Cao Rui personally arrive with reinforcements, and Sun withdraws, as do Lu Xun and Zhuge Jin.

Gongsun Yuan is under attack by Wei's general Sima Yi in 238.

Sun Quan, despite his prior rage against Gongsun, correctly judges the situation as one where he might be able to take advantage if Sima Yi were initially unsuccessful, and does not immediately refuse Gongsun's request for help.

However, as Sima Yi is able to conquer Gongsun Yuan quickly, Sun Quan never launches the major attack that he had considered were Sima to have gotten stuck in a stalemate with Gongsun.

In this year, he also recognizes the manner in which his head secretary Lü Yi had been falsely accusing his officials, and has Lü executed; he then further confirms his trust in the high level officials by personally writing an emotional letter to Zhuge Jin, Bu Zhi, Zhu Ran, and Lü Dai, blaming himself for the recent problems with his administration while urging them to speak out honestly whenever they see faults in him.

Sun Quan appoints his son Sun He, born to Consort Wang, crown prince in 242.

However, he also favors another son by Consort Wang, Sun Ba, the Prince of Lu, and permits Sun Ba to have the same staffing level as the crown prince—a move to which a number of officials object, as encouraging Sun Ba to compete with Sun He, but Sun Quan does not listen to them.

Sun Quan launches the last major assault of his reign against Wei in 241, in light of Cao Rui's death in 239, but he rejects a strategy offered by Yin Zha to attack Wei in a coordinated effort with Shu on four different fronts, and the campaign ends in failure.

The death of the crown prince Sun Deng later in 241 leaves open the issue of succession and appears to mark the start of a precipitous decline in Sun Quan's mental health.