The laser ranging system with hundreds of kilohertz measuring frequency and sub-centimeter level accuracy is one of the hotspots in the research of laser ranging. The principle and method of realizing laser ranging system are analyzed based on picosecond pulsed laser. According to the utmost narrow pulse width, the method of double thresholds leading-edge timing discrimination and width control method of digital signal generated by voltage comparator are applied. Coupled with high accuracy time to digital chip TDC-GPX, it can achieve the requirement of system. Experiments show that the system is stable and reliable, the measuring frequency can be up to 500 kHz, and the ranging accuracy is between 4 mm and 10 mm.