Stress refers to stress in physics, that is, a kind of pressure, which has the meaning of stimulation and reaction in biology. Post-traumatic stress disorder (PTSD) is a mental disorder that occurs within a few days to six months after an individual is exposed to an unusually strong traumatic shock or trauma. Human events such as rape, abuse, violent assault, kidnapping, major traffic accidents and severe natural disasters such as strong earthquakes and tsunamis can cause mental disorders. Post-traumatic stress disorder (PTSD) is one of the few mental disorders with relatively clear etiology and unique clinical features, such as frequent flashbacks of traumatic events and hyper vigilance. This paper briefly introduces and reviews the cognitive theory of post-traumatic stress disorder. And it also outlines various famous academic experiments on these theories, elaborates on the breakthrough theories made by these academic experiments in these fields, and their contributions to psychiatry and its subsequent treatment. This paper finds that some theories about the cognitive theory of PTSD still have some limitations and need to be further perfected.