Abstract: We present our research about the imaging quality of underwater imaging systems based on the angle configuration of the light source. Supposing the distance between the light source and the target is equal to that between the camera and the target, we developed better transfer functions of the contrast degree and the signal-to-noise ratio (SNR). By defining that the distance from camera to the target is invariable, we described the dependence of the contrast and SNR on the angle configuration of the light source, we also gave some curves of this relationship. We analyzed the impact on the imaging quality caused by the hypothesis and the approximate. Experimental results agree with our analysis.