ITC/USA 2009 Conference Proceedings / The Forty-Fifth Annual International Telemetering Conference and Technical Exhibition / October 26-29, 2009 / Riviera Hotel & Convention Center, Las Vegas, Nevada / In reentry measurement, we need to measure the track of reentry vehicle. For the speed of target is very high, it is difficult for traditional positioning system to capture and track the target. TDOA (time difference of arrival) positioning system is used in reentry measurement. The position of target is calculated by using time difference of arrival. This paper introduces the principle of reentry TDOA positioning system. The key technology is synchronization of ground stations' clocks. The implementation of clock synchronization using low-cost commercial GPS receiver is presented. The sources of errors in the existing telemetry system, corresponding precision and experimental results are presented. Some methods, which are used to improve the precision, are proposed at the end of this paper.