In spite of these successes there was a vehement dispute among the highest strategists of Qin about the way to subdue the armies of Chu 楚, the mighty competitor in the south. While Li Xin 李信 would only allow 200,000 troops, Wang Jian was sure that an army of less than 600,000 troops would not do. King Ying Zheng 嬴政 (r. 246/221-210 BCE) was inclined to the opinion of Li Xin, the younger person and the more brave of the two, and dispatched an army of 200,000 under the command of Li Xin and Meng Tian 蒙恬.
Wang Jian feigned being sick and withdrew to his manor in Pinyang 頻陽. In the beginning the army of Qin could acheive some victories over the troops of Chu, but the latter soon stroke back and defeated the forces of Qin in a battle, with seven high commanders being killed. This heavy defeat opened the eyes to the king, and he personally traveled to Pinyang to ask Wang Jian to resume his service for Qin.
Wang Jian consented, and at the head of an army of the envisaged 600,000 he attacked Chu in 224. After a protracted battle at Ji 蘄 he annihilated the total forces of Chu and was able to kill general Xiang Yan 項燕.
A year later, Wang Jian and general Meng Wu 蒙武 were able to capture King Fuchu 負芻 of Chu (r. 227-223). The state of Chu was incorporated into the state of Qin as commandery Chu 楚郡.
In 222, Wang Jian submitted the rest of the southern states, pacified the hundred Yue, i. e. the state of Yue 越, and installed the commandery of Guiji 會稽. His son Wang Ben 王賁 and his grandson Wang Li 王離 also stood in the service of Qin.