A Position-Sensitive Detector (PSD) was used to measure two-dimensional displacement with high precision. A combination of three two-dimensional PSDs can implement measurements of six-degree-of-freedom relative displacement and angle. The measurement system mainly comprises three PSD sensors (including PSD photosensitive surface and light-emitting tube), low noise signal conditioning, and an Analog to Digital(AD) acquisition circuit. Three PSD orthogonal layout schemes were used to calculate the displacement and angle of relative motion through the spot position of three PSD photosensitive surfaces. A six-degree-of-freedom PSD calibration and test system was designed for the calibration of the PSD measurement system center offset and light tube installation error. The test results show that the measurement range of the PSD measurement system is better than ±10 mm and ±2.5°. The noise error of the PSD measurement system after calibration is 0.1 mm and the angle is 0.02°, while the absolute displacement error of the measuring system is less than 0.5 mm and the angle error is less than 0.14°. This proves that the system meets the requirements of 0.5 mm and 0.5°. In addition, the environmental adaptability of the PSD sensor was evaluated. It can satisfy the system requirements of noncontact, online, real-time, higher precision, and rapid speed, as well as strong anti-jamming and stabilization. The system is successfully used in the space microgravity active vibration isolation system of the Tian Zhou 1 cargo ship for relative motion measurement.