Firstly, we introduce the linearity of the power amplifier. Secondly we describe the AM-AM, AM-PM characteristics curve. At last, we analysis and stimulate the effect which power back-off brings about in the communication system with OFDM modulation. 先是对功率放大器的线性度进行了介绍,继而描述了AM-AM与AM-PM特性曲线,最后就功率回退方法对60GHz通信下OFDM系统产生的影响进行了分析与仿真。