The intersatellite laser interferometric range measurement system is the core load of the next generation low-low tracking gravity measurement satellites. This system requires measurement accuracy of interstar distance change to the extent of a nanoscale. Considering this request, a laser interferometric ranging system with a corresponding answer-and-forward system is designed. The system measurement principle and frequency transmission relationship are deduced according to the system composition and the working principle. The measurement error items in the laser interferometric range measurement system are decomposed at the top-level analysis. The mathematical evaluation model is established for each error item, and numerical analysis is conducted. According to the laser interferometric range measurement system, the interstar distance change measurement accuracy greater than 7.5 nm/Hz^1/2@0.1 Hz (0.1 Hz is Fourier frequency point) is finally realized, to meet the requirements of the next generation low-low tracking gravity field high-precision inversion for intersatellite laser interferometric ranging system.