OBJECTIVE： To evaluate clinical efficacy through comparing the change of CT image in infrapatellar fat pad before and after Xiaoding ointment in the treatment of acute patellar bursitis of knee joint. METHODS： 73 patients with acute patellar bursitis were randomly divided into observation group （39 cases） and control group （34 cases）. Observation group was given Xiaoding ointment for local application， qd， 7 d as a courses， 3 courses in total； control group was given triamcinolone acetonide 30 mg after the extraction of articular cavity effusion， once a week， totally for 3 times. All patients of two groups underwent knee CT examination for observation of the infrapatellar fat pad and articular cavity effusion volume change before and after treatment. Clinical efficacies were compared between 2 groups. RESULTS： CT image alterations of treatment group showed that infrapatellar fat pad density were decreased， anteroposterior diameter， vertical diameter， internal to external diameter were significantly reduced. The total effective rate of treatment group was 92.31％， which was better than that of control group （88.24％）， with statistical significance （P＜0.05）. CONCLUSIONS： Xiaoding ointment demonstrate markedly curative effects in the treatment of acute patellar bursitis， and CT image is an effective method for diagnosis of infrapatellar fat pad.