The report provides the principle and advances of range-gated underwater laser imaging technology. A novel prototype underwater laser imaging system has been designed and developed. The range-gated technique is one of the effective methods to decrease the backward scattering of the water. By using the lower attenuation window for the water in the visible light spectrum, pulse laser with the blue-green wavelength has been adopted as an illumination source and CCD as the receiver. The range-gated underwater laser imaging system has been successfully fulfilled. The system can decrease the influence of backward scattering and at the same time the system can improve target luminance. The detail schematic principle and realization scheme have been analyzed. It has been found that the range-gated underwater laser imaging system could improve the imaging quality and the imaging distance by conveniently adjusting the pulse delay and the pulse width. It has been become one of the key techniques in underwater laser imaging research field.