2.7～3μm laser, which has the important value of medical and military applications, are obtained from the transition 4I11/2 →4I13/2 with rare earth Er3 + as the active ions and YSGG, GGG, GSGG, YAG, YLF as the matrix material. Under 790 nm pump, the Er:YSGG as laser material can produce 2.79 μm stimulated emission. By building the rate equation of Er:YSGG energy level transition, the system characteristics of rotating mirror Q-switched laser were analyzed and numerical simulations were carried out. Result of the numerical simulations comprehensively shows the influence of system variables on the performance of rotating mirror Q-switched laser. These conclusion will provide theoretical guidance for the laser design and improvement of similar experiment.