Abstract: Gate length of range-gated imaging system as a key characteristics was theoretically and experimentally analyzed in this paper. A frequency doubled 532 nm Nd:YAG laser that the pulse full width at half of maximum(FWHM) was 20 ns and ICCD was used to build up range-gated imaging system, what effects on imaging performance with the change of the bandwidth of the gate signal and gate delay time were studied through a straightforward method, which place white board signs at relevant distances in the field of view. Examples of imagery collected for different range and gate conditions will be presented and discussed with respect to the intensity at the signs in a gated images. When gate signal width is 10 ns, measurement result of the effective temporal gate length is 35 ns.