Colorectal cancer is one of the most common cancers in the world. Recently, with changes of lifestyles and diet structures, more and more people suffer from obesity. A large amount of studies on epidemiology show that risk of colorectal cancer is close related to obesity. However, as for that if obesity influence the prognosis of colorectal cancer, research results are all different. Hereby, this paper explains the prognosis relationship between obesity and colorectal cancer. At present, there are both arguments and counter-arguments clinically. Most of research results show that obesity influences the prognosis of colorectal cancer to a great extent and analyze the possible action mechanism that obesity influences the prognosis of colorectal cancer, including resistance to insulin or hyperinsulinemia from obesity, chronic inflammation caused by obesity and excessive expression of fatty acid synthase (FASN). At last, it concludes that as the main dangerous factor and poor prognosis factor of colorectal cancer, obesity influences deaths and recrudescence of colorectal cancer to some extent.