For the characters of long-distance flight target and the stringent requirements of time synchronization standard in time-measurement of different locations, we put forward a high-precision time-measurement system based on GPS. The system combines GPS time service with local crystal oscillator clock, which uses GPS second pulse to make time synchronization and local crystal oscillator clock to measure precise time of the start and stop of flight target. Meanwhile, it gives a way to realize high-precision time synchronization from monitoring and compensating GPS second pulse. Experiments show that the system is able to control the deviation less than 300 μs within 400 s’ measurement, and the equivalent precision can reach 7.5×10-7.