The model for a new kind of underwater laser imaging system is proposed. The quantity relationships of imaging distance and quality of the system with the main system parameters such as the scattering angle of light beam, the visual angle and open time of gate of receiver are calculated. The results show that the imaging quality and distance can be increased by decreasing the influence of background-lights and increasing the quality of pulse-light. The theoretical value of imaging distance for the new kind of underwater laser imaging system in the ordinary seawater can reached 25 times of the attenuation lengths, which is as 4～5 times long as that for the synchronous scanning and range-gated systems.