In order to meet the requirements of measuring high-velocity moving dim small targets, a velocity measurement method based on single-frame multiple local exposures is designed. The influence of key parameters on measurement frequency is analyzed theoretically, and the expression of gray imaging model of laser illuminated target is deduced. Using pulsed laser as local exposure light source and timing base, the target image with time stamp is generated in a single-frame image for many times. A velocity measurement model of single-frame multiple local exposures is established, and the spatial positioning and velocity measurement of small dark targets are realized by using monocular vision and laser ranging data, which breaks the upper limit of the measurement frequency of high-velocity camera and improves the measurement accuracy. Velocity measurement simulation experiment is carried out on a target with a velocity of 1500m/s, and the results showed that the velocity measurement error is less than 0.7%. The prototype experiment proves that the relative velocity error of target is less than 2.5% compared with the velocity of standard velocity target launcher in low velocity conditions, and the system has low cost and good maneuverability, which meets the requirements of engineering precision.