The traditional laser projectile velocity system is susceptible to the impact of high-temperature frontal shock luminescence and space electromagnetic field, resulting in a decrease in the system’ s signal-to-noise ratio. In order to obtain high-quality signal waveforms, a new type of laser projectile velocity measurement system that can be used for light-gas gun is designed, and improved methods of laser light path and photoelectric conversion circuits are proposed in this paper. The use of optical fiber to guide the laser avoids the use of long leads and enhances the system’s anti-interference ability. A solid-state laser with an output power of 40 mW was selected as the system light source, and a composite laser receiving probe with filtering and focusing functions was designed to increase the signal light intensity. The noise and bandwidth of the measurement circuit are analyzed in detail, and the photoelectric conversion circuit is improved and optimized. The signal-to-noise ratio of the measurement circuit is increased to 98 dB. The actual test results show that the signal waveform quality obtained by the laser projectile velocity measurement system is good, and the relative expanded uncertainty of the velocity measurement result is 0. 73%, which meets the requirements of the light-gas gun projectile velocity measurement system.