The objective of this article is to discuss skeletal muscle fibers transformation mechanism by blocking CaN/NFAT (calcineurin/Nuclear factor of activated T cells) channel and endurance training.Methods: 40 adult healthy Spraque Dawley (SD) rats were randomly divided into 4 groups: Control group (C), Cyelosporine group (S), Training group (T) and Cyclopsorin-training group (ST).T and ST group rats were trained in treadmill, speed 28 m/min, 60 min/day, 6 days/week, for 12 weeks.During the last 3 weeks, ST and S group rats were treated with cyclopsorin (CsA) (15 mg/kg/day).The soleus MHCs(myosin heavy chains) composition was determined by SDSPAGE method, Immunohistochemical method for detectining MyoD and Myogenin expression, Western blotting for measuring the cytoplasm NFATC1 protein expression, CaN activity was decided by detecting its phosphorus content.The results show that the CaN activity in S and ST groups were significantly lower than C group (P<0.05)(P<0.01), Among of these, the ST was lower, and lower than T group.However, there is no obvious difference between T and C group;The cytoplasm NFATC1 expression was lower in T group than in C group (P<0.05),and there existed a greater reduction in ST group (P<0.01);The percentages of MHC isoforms in difference condition were shown in table 2, no significant differences were seen in Cyclosporine, endurance training and control groups.