High ranging speed, wide measurement range, and high accuracy are the trends of modern satellite/lunar laser ranging (SLR/LLR) . High precision event timer is demanded as the timing unit in such a laser ranging system. The time interval timing principle of event timer is analyzed.A high-accuray event timer is realized and designed based on time-to-digital converter (TDC) and field programmable gate array (FPGA) technique, for which the TDC chip is used to measure fine time and the FPGA chip is used to measure coarse time and control the whole timing system. Signal period measurement experiment is performed,showing the standard deviation better than 50 ps, the systematic error less than 11 ps, the measurement range of 24 h,the temperature drift below 100 fs/℃, and temporal stability lower than±3 ps/h.