Abstract: As an important issue in the area of underwater laser imaging, how to completely analyze the detection capability of the range-gated underwater laser imaging system, was introduced in this paper. For the purpose of evaluation, according to the imaging mechanism, the analysis of target and background radiation was reported, along with the analysis of backscattering of seawater, the characteristic of range-gated and the performance of laser transmitter and receiver. Then, the detection sensitivity model of the range-gated underwater laser imaging system was established based on the beam spread function(BSF). This model could be applied in practice as the ratio between seawater scattering coefficient and attenuation coefficient ranges from 0 to 1. In addition, simulations were done to analyze the beam divergence, the optical system aperture, the gate width of intensified CCD camera and other factors that influence the imaging systems detection capability. The results show that the maximal detection depth of such a system can be achieved when gate width equals to laser pulse width. Thus, this work can provide a theoretical basis for designing the underwater laser imaging system and optimizing the system parameters.