Based on the nonliear mathematical model for the steady state operation of a liquid rocket engine, the effects of each interfering factor on the parameters of liquid rocket engine are calculated. The comparative analysis is carried out for the effects of the interfering factors on the engine parameters by using both nonlinear method and method of small deviations. The results obtained can be used for the analysis of the pump-fed gas generator cycle liquid rocket engine test results，the reliability analysis and the fault analysis, and also for bringing to light the variation of the engine parameters with various interfering factors.