Abstract: In order to both reduce the number of scanning frames and ensure the image quality,a variable step scanning method was put forward for range-gated underwater laser imaging.Firstly,the focal length,focal position of the receiver lens and the system scanning scope were defined based on both radiation detection theory and the principle of depth of field.Then the step size of delay and the width of the gated pulse were calculated according to the time-domain broadening of underwater laser pulses. Finally,the simulation and experiments were conducted.The experimental results show that the range-gated imaging system based on the proposed scan method can scan over the scope from 15m to 48.6m with 7 pulses imaging,and the image quality is kept at the same time.This proves the validity of this method,and provides an attempt for the actual application of range-gated technique in underwater imaging.