Objective To study the effect of short⁃duration mechanical ventilation on the function of the dia⁃ phragm in rats with different degrees of sepsis. Methods Experimental groups included SHAM group，CLP50% group，CLP50%+MV6h group，CLP75% group and CLP75%+MV6h group. Biological signal acquisition system was used to detect diaphragm contraction force and compound muscle action potential（CMAP）；HE staining was used to observe muscle fiber cross⁃sectional area（CSA）；TUNEL method was adopted to detect apoptosis；ELISA was used to detect serum inflammatory factors；the expression of muscle atrophy⁃related proteins was detected by Western blot. Results In the CLP50%+MV6h group，compared with the CLP50% group，diaphragm contractility was decreased， and serum IL ⁃6 levels and atrophy ⁃ related protein levels were increased. In the CLP75%+MV6h group，compared with the CLP75% group，CMAP amplitude was decreased and duration was prolonged；contractility was decreased， CSA was reduced，inflammatory factor levels were increased，and atrophy⁃related protein levels were increased. Com⁃ pared with the CLP50%+MV6h group，the CLP75%+MV6h group showed decreased CMAP amplitude and increased duration，decreased contractility，decreased CSA，increased inflammatory factor levels and atrophy ⁃ related protein expression，and increased apoptotic index. Conclusion In septic rats，a short⁃term of mechanical ventilation could exacerbate diaphragmatic dysfunction，which became more pronounced as the degree of sepsis increased.