The water has a strong absorption and scattering of light radiation, resulting in a certain depth of the underwater world in the dark. Therefore, underwater optical detection technology based on active lighting has become the main mode of deep-sea photo detection. Using a 532nm narrow-pulse laser and a self-built gain CCD system to form a underwater laser rang-gated imaging system, the forward and backward scattering are modeled and analyzed. Underwater laser rang-gated imaging system, was studied by laser pulse jitter, thus lead to the door of the control signal, the open time (earlier/later), the relationship between secondary scattering and image contrast curve, puts forward an optimal pulse with door control strategy. The correctness of the model is verified by the method of simulation and calculation of the relative ratio of the images acquired by the actual underwater laser distance gating imaging system. The results show that when the imaging system is not saturated, the image quality is best when the gate and the laser pulse are optimally matched. The effects of early opening and delayed opening on the image quality are different, and the duration of the gate opening is equal to the laser pulse width. At that time, the image quality is not optimal, and the effects of laser pulse jitter and secondary scattering are not all unfavorable. Based on the model, the opening time and the gate opening time are determined according to the contrast curve. It is generally advantageous to open the door lagging behind, and the duration of the gate opening should be 1- 3 times the laser pulse width.