In Romance of the Three Kingdoms, Cao Cao died because of a head wind, a headache. He asked Hua Tuo to treat him. Hua tuo said that he would open his skull, but he refused to say that it would hurt him and kill Hua tuo. However, romance is a novel and may be inaccurate.
The real cause of Cao Cao's death should start from Wancheng. After getting Wancheng, Cao Cao and Zhang Xiu's uncle's wife became enemies. Zhang Xiu secretly arranged for Hu Cheer to steal Dian Wei's double halberd and prepare to attack Cao Cao at night. However, Dian Wei fought to the death for Cao Cao and eventually died with Wancheng. Its heroism is amazing and admirable. Deeply grateful, Cao Cao reburied it and adopted its son. After that, Cao Cao got sick, lurked for a while, then had an attack, and finally Cao Cao died.