Abstract：Objective：To observe the knee injury of amateur marathon runners after race and the clinical effect of Shujin Waixian Granules by magnetic resonance imaging (MRI). Methods：The amateur marathon runners were examined by MR 24 hours after the race，and 21 patients with knee injury and abnormal knee were screened by MRI. They were divided into the trial group and the control group according to random number table method，with 11 cases (18 joints) and 10 cases (18 joints) in each group. The control group only intervened with joint braking and rest，and there was no medicinal treatment. The trial group was given the fumigation with Shujin Waixian Granules. After 7 days of observation and treatment，the clinical effects and knee MRI results in the two groups were compared. Results： Abnormal MRI results were found in 36 knee joints of 21 cases：there were 20 cases of joint effusion or soft tissue swelling (11 on the right side and 9 on the left side)，5 cases of anterior cruciate ligament injury (3 on the right and 2 on the left)， 8 cases of medial collateral ligament injury (6 on the right and 2 on the left)， 6 cases of lateral collateral ligament injury (2 on the right and 4 on the left)，and 3 cases of bone marrow edema (2 on the right tibial plateau and 1 on the left internal condyle). After treatment， the total effective rate of clinical effect was 83.33% in the trial group and 27.78% in the control group，the difference being significant (P＜0.05). The total effective rate of MRl was 88.89% in the trial group and 33.33% in the control group，the difference being significant (P＜0.05). Conclusion：MRI can effectively evaluate knee joint injury of amateur marathon runners after race，and the therapeutic effect of Shujin Waixian Granules on knee joint injury after marathon is certain.