The influence of detector’s gain on laser disturbing effect has been investigated in the experiment. We firstly measure the noise distribution and grey scale of output image under the different CCD gains, and then define the variable relation of noise grey scale with the increase of CCD gain. According to comparing laser spot image and grey scale distribution under the different gains, it is secondly found that the increase of CCD gain can amplify the weak signal around laser main spot, add the number of saturated pixel and enhance laser disturbing effect. The variable relation between signal grey scale and CCD gain has been also defined by calculating signal grey scale. At last, it is can be achieved to simulate laser disturbing effect under the different gains based on the relation of signal/noise grey scale and CCD gain. The research results can provide technical support and theoretical reference for evaluating laser disturbing effect of electro-optical imaging system under the different gains.