This paper discusses the impact of the adjacent channels on the 1-dB compression point, the IP3 and the IP5 of Radio Frequency (RF) amplifier by n-tone test. By combining the theoretical derivation and software simulation, the model analysis for the third/five order polynomial nonlinear amplifier has been achieved. Moreover, the control variable method is adopted to draw the curves for the input/output signals. The research shows that the 1-dB compression point, the IP3 and the IP5 drop as n increases, and they all have symmetry for a given n. The fifth-order polynomial nonlinear amplifier model is proposed, the research shows that the adjacent channels have a great impact on the 1-dB compression point, the IP3 and the IP5 of the desired channel. This effect must be taken into account in actual RF amplifier designs and wireless communication architectures.