To accurately measure the zero signal of rockets during takeoff, a measurement method was put forward herein combining laser active imaging and range-gated technology, under which the zero signal was obtained by calculating the change in optical flow and then the amount of displacement. Existing zero signal measurement methods were analyzed to determine the range-gated ICCD imaging method, and combined with the feature of the target rising vertically, an anti-light interference algorithm was proposed combining the target contour and HS optical flow. Results show that as the simulated target is rising in uniform velocity, when the light changes little, either edge detection or HS optical flow detection algorithm could detect the upward trend of the target independently; when the light changes drastically, both edge detection and HS optical flow detection algorithm show serious errors, while edge detection combined with HS optical flow algorithm eliminates the interference inside the target, and the target pixel displacement amount obtained is basically consistent with the real ascending amount with the error in sub-pixel. If the image frame frequency is 25 fps, the time accuracy is 80 ms, which is in full compliance with the requirements of zero signal extraction.