Abstract: Waveform Distortion Problem of input signal ui in the Common-emitter amplifier is analyzed in this paper.In actual cases,the input waveform will be top distortion if triode operates in the saturation region,because the input current is too large and the emitter junction is deemed as a positive onset PN junction.On the other hands,when the transistor work in the cut-off area,the emission junction reverse bias,base virtual,the input signal ui will not produce significant distortion.