When Sun Ce died in 200, Cheng Pu, along with Zhang Zhao and others, pledged allegiance to Sun Quan (Sun Ce's younger brother) and travelled around Sun Quan's territories to attack those who refused to submit to the new lord. Under Sun Quan, Cheng Pu fought at the Battle of Jiangxia in 208 and aided in the conquest of Le'an () when he passed by Yuzhang (). He later replaced Taishi Ci as the commander of a garrison at Haihun (). During the Battle of Red Cliffs of 208-209, Cheng Pu and Zhou Yu served as the Left and Right Commanders of Sun Quan's army respectively, and scored a major victory in the battle against Cao Cao's forces. Cheng Pu and Zhou Yu also led Sun Quan's forces in the subsequent Battle of Jiangling, a follow-up to the Battle of Red Cliffs, and defeated Cao Cao's general Cao Ren. After those battles, Cheng Pu was promoted to Major-General () and he served as the Administrator () of Jiangxia Commandery (), with the commandery capital at Shaxian County (), and was in charge of four counties.