Abstract: Power amplifier nonlinear distortion results in intermodulation distortion and adjacent channel interference, which affect the performances of communication system directly. Based on the model of PA, how to describe and analyze its nonlinear is important. Taylor series method, Volterra series method and harmonic balance method are discussed in this paper, experiment and simulation results are also given, which show it is feasible and useful to use these methods to analyze the effect of PAs according their nonlinear level.