The purpose of this paper is to build a risk assessment index system of fitness running for college students. Through consulting relevant literature and interviewing experts, the first, second indexes of fitness running risk are screened and determined. First of all, based on the social combustion theory, the occurrence of sports risk is divided into three parts: combustion substance, accelerant and combustion point, and various influencing factors in the risk of college students’ fitness running can be regarded as “accelerant” in the three elements, “accelerant” is a crucial part of the three elements. Based on the key factor of “accelerant”, a complete risk assessment system of college students’ fitness running is constructed by calculating its weight value through AHP. The research shows that the risk assessment index system of fitness running for college students can effectively reflect the risk factors of fitness running, and carry out risk assessment on this basis to help improve the cognition of sports risk for college students. The risk assessment index system of fitness running constructed in this study is a scientific and practical evaluation tool, which can help college students fully understand the factors that will cause sports injuries during fitness running and reduce the sports injuries of college students during running.