Abstract: For the spacecraft in Halo orbits around L₂ point in Sun-Earth system, firstly, the kinematics equation of spacecraft in initial frame and rotating frame (and celestial navigation model whose measurement is starlight angle were presented. Secondly, the celestial navigation model whose measurement is starlight angle was established; thirdly, an extended Kalman filter (EKF) algorithm was used to estimate of the position of the spacecraft; finally, the performance of the system using different kinds of statement and measurement was analyzed based on the Cramér-Rao low bound method. Simulation results show that some factors that influence largely on the precision of position estimation are pointed, which includes navigation coordinate system, the major celestial body, the number of observing the stars and filter observation time. The results of the above factors impacting on the precision of celestial navigation are analyzed based on libration point orbit kinematic characteristics.