〔Abstract〕 Objective To investigate the effect of ultrashort wave intervention on the articular function, joint capsule morphology, expression of transforming growth factor β1(TGF-β1) and connective tissue growth factor(CTGF) of rabbit knee extension contracture, and to explore the process of knee joint contracture. The changes of joint capsule fibrosis and the mechanism of ultrashort wave therapy were preliminary discussed. Methods New Zealand rabbits were randomly divided into 4 groups and treated with different interventions: a blank control group(O group) without any treatment, a simple fixed group(P group) killed immediately after 8 weeks of fixation, and removed after 8 weeks of fixation, the natural recovery group(group N) with 4 weeks of free movement of gypsum, and the ultrashort wave treatment group(group M) with 4 weeks of ultrashort wave treatment after removing the plaster for 8 weeks. Immediately after the rabbit was sacrificed, the knee mobility was recorded using a joint mobility measuring instrument after myotomy. The posterior joint capsule was selected from the group, Masson staining was used to detect the expression level of collagen in the posterior joint capsule of each group, semi-quantitative RT-PCR was used to detect the mRNA expression of TGF-β1 and CTGF in the joint capsule; Western blot was used to detect the joint capsule in the posterior knee joint TGF-β1 and CTGF protein expression levels. Results Compared with group O, the movement of knee joint in group P decreased after myotomy(P<0.05), the percentage of collagen in the joint capsule behind the knee joint, and the protein and mRNA expression levels of TGF-β1 and CTGF increased(P<0.05). Compared with group P, there was no significant difference in knee joint mobility and CTGF protein expression level after myotomy in group N, and CTGF mRNA expression level increased(P<0.05). The percentage of collagen in the joint capsule and the expression of TGF-β1 protein and mRNA in the posterior knee joint decreased(P<0.05). Compared with group P, the activity of the knee joint increased after myotomy in group M(P<0.05), the percentage of collagen in the joint capsule behind the knee joint, the protein and mRNA expression of TGF-β1 and CTGF decreased(P<0.05). Compared with the N group, the knee joint activity after the myotomy in the M group increased(P<0.05), the percentage of collagen in the joint capsule behind the knee joint, the protein and mRNA expression levels of TGF-β1 and CTGF became lower(P<0.05). Conclusion Ultrashort wave may reduce the expression of TGF-β1 and CTGF in the joint capsule, reduce the fibrosis of the posterior joint capsule of the knee joint, and then effectively improve the progress of straight knee contracture.