Abstract: To obtain high precision position of spacecraft,a 3-D relative position measurement model is established,and an algorithm to calculate the 3-D position based on a single-baseline same-beam interferometry (SBI) is proposed by using Least squares. SBI measurements between TT&C antenna and directional antenna of Chang'E-3 lander are conducted to verify the proposed model and its calculation algorithm. Results show that the random error of SBI delay is about 0.225 ps (0.07 mm),the distance error between TT&C antenna and directional antenna is about 0.216 m, and the direction error between them is about 30.4°, which will be used for high precision relative measurement between sub-spacecraft of Chang'E-5 and other deep-space exploration missions.