The ranging precision is an important indicator to measure the performance of laser rangefinder. A detection system of ranging precision for 1 064 nm, 1 540 nm, and 1 570 nm wavelength rangefinder was introduced. The system consists of distance simulator and laser radiation simulator. Radiation simulator can generate an echo pulse with width among 5 ～250 ns and the maximum peak power 0.1 W. FPGA-based distance simulator can realize distance simulation during 50 m～990 km. The closed-loop detection method between radiation simulator and distance simulator is proposed and realized. According to the method, the fixed error of detection system is measured and eliminated. The detection results show that the distance simulation error is less than 1 meter in full simulation scale.