The Battle of Huoyi is fought in China on September 8, 617 between the forces of the rebel Duke of Tang, Li Yuan, and the army of the ruling Sui Dynasty.

Li Yuan, with an army of ca.

25,000, is advancing south along the Fen River towards the imperial capital, Daxingcheng.

His advance is stalled for two weeks due to heavy rainfall and he is met at the town of Huoyi by an elite Sui army of 20,000 (or 30,000) men.

Li Yuan's cavalry, under the command of his two eldest sons, lures the Sui out of the protection of the city walls, but in the first clash between the two main armies, Li Yuan's forces are initially driven back.

At this point, possibly due to a stratagem on Li Yuan's behalf, the arrival of the rest of the rebel army, or to the flanking maneuvers of Li Yuan's cavalry, which had gotten behind the Sui army, the Sui troops collapses and routs, fleeing back towards Huoyi.

Li Yuan's cavalry, however, cuts off their retreat.

The battle is followed by the capture of weakly defended Huoyi, and the advance on Daxingcheng, which falls to the rebels in November.

In the next year, Li Yuan deposes the Sui and proclaims himself emperor, beginning the Tang Dynasty.