History books call him "a brilliant and resourceful man, a world miracle". Cao Cao praised him for his knowledge and was his "Zuo Qi".
In the fifth year of Jian 'an (200 years), Cao Cao decided to destroy Liu Bei, who was unstable in Xuzhou, in order to avoid being attacked before and after fighting Yuan Shao in the future. At that time, people were afraid that Yuan Shao would take the opportunity to capture Xudu, and then he would retreat without fighting and lose his stronghold. Cao Cao also had doubts, so he asked Guo Jia for advice. Guo Jia analyzed: "Yuan Shao has always been indecisive and won't react quickly. Liu Beixin has not returned, and his foothold is unstable. He must attack it quickly. He is sure to fail. Then return to Li to deal with Yuan Shao. This is the best opportunity to be attacked by both sides and must not be lost. " Therefore, Cao Cao led people to the East Expedition, defeated Liu Bei, captured Liu Bei's wife, and captured Guan Yu, and then broke the East China Sea bandits who joined hands with Liu Bei. As Guo Jia expected, Liu Bei was defeated before Yuan Shao could react.
Just as Cao Cao and Yuan Shao were at loggerheads in Guandu, another disturbing news reached Cao Ying: Sun Ce, a hero of Jiangdong, was preparing to send troops to attack Cao Cao's base in Xudu. Cao Cao, who was already at a disadvantage in the stalemate with Yuan Shao, could not spare more troops to defend Xu Du. Once Xu Du falls, Cao Cao's camp will immediately fall apart. This is the most turbulent period of Cao Cao's camp, and many people began to secretly flatter Yuan Shao, ready to leave a way out for themselves.
At that time, there were many private correspondence between Cao Jun and Yuan Shao. After the Battle of Guandu, many Han bamboo slips were found in Yuanying. At this critical moment, Guo Jia predicted: "Sun Ce just annexed Jiangdong, and all the people he killed were heroes. He is a man who can make people die. But Sun Ce is reckless and not good at prevention. Although he has a population of one million, he came to the Central Plains alone. If an assassin lies in ambush, he is only one man's enemy. In my opinion, Sun Ce must have died at the hands of an assassin. " Sun Ce reached the river, and before crossing it, he was killed by the protege of his enemy Xu Gong. This may be a coincidence, but it does add to Guo Jia's ingenuity.
In the seventh year of Jian 'an (202), Yuan Shao, who was defeated in the battle of Guandu, died, and Cao Cao pursued his two sons, winning Lien Chan. Jun people want to attack the Second Yuan, but at this time, Guo Jia, who had argued for the northward advance, pushed his way through the crowd, found a new way and suggested withdrawing troops. He analyzed the contradiction between the Yuan brothers for Cao Cao, saying: "Yuan Tan and Yuan Shang have always been at odds, and there are advisers like Guo Tu in the middle, which will inevitably turn against each other. It is better to levy Liu Biao in the south first, wait for it to change, and then attack it. "
Guo Jia suggested that Cao Cao feint Liu Biao south and "wait for it to change". Sure enough, just after Jun returned to Xuchang, the news of the bad weather in Yuan Junsheng came. Cao Cao took the opportunity to return to the north, split Yuan Tan and Yuan Shang in two, and Yuan Yi escaped. Thanks to Guo Jia's clever plan, the battle was won easily and smoothly.
In the ninth year of Jian 'an (204), Guo Jia was named Jingyang Tinghou.
In the tenth year of Jian 'an (205), Guo Jia suggested that Cao Cao should recruit and reuse more celebrities from Qing, Hebei, Youzhou and Sizhou to win the hearts of the people and completely consolidate control and resistance. Cao Cao took his advice and even reused Chen Lin, who once vilified himself. It is really valuable.