Abstract: Cancer has become the second leading cause of morbidity and mortality in the world.The evidence suggests that 9% to 19% of the cancer incidence in Europe is due to lack of physical activity.In order to decrease the risk of cancer, lifestyle intervention, increasing the physical activity, may become a cost-effective and long-term cancer control option.The aim of this study was to systematic review the association of physical activity/exercise and the risk of cancer, and the potential biological mechanism of physical activity/exercise on carcinogenesis, which will provide theoretical support to promote and advocate physical activity as a key component of cancer prevention and the promotion of healthy lifestyles.Methods:In this paper, we searched the keywords “physical activity”, “leisure activity”, ”exercise”, “exercise”, “cancer”, “risk”, “m ec hanism” and “biological changes” in the databases of Pub Med and Highwire.A total of 23 articles were included, which were published in 2012-2017.Results:1) Whether or not obesity, the increase of physical activity was with associated with reduced risk of many types of cancer.2) The most likely biochemical mechanisms of physical activity to reduce cancer risk include direct anticancer pathway and indirect anticancer pathway.Direct anti-cancer mechani sms include metabolic hormones, epigenetic effects, oxidative stress, immunity, chronic inflammation and so on.Indirect anti-cancer mechanisms include:weight loss and estrogen, adipokines, vitamin D and sunlight exposure, elevated mood and so on.Conclusion:1) It is recommended that physical activity be added as an effective intervention to prevent cancer risk.2) The physical activity reduces the risk of many types of cancer through a direct anticancer pathway and indirect anticancer pathway.