Abstract: Celestial navigation based on star angle is a classical autonomous navigation method for spacecraft. By measuring the angular relationship between spacecraft, near celestial bodies and background stars, the current position and velocity information of spacecraft can be deduced. However, the effect of general relativity causes the starlight from a star to be somewhat deflected as it passes through a massive object, and special relativity allows high-speed spacecraft to observe stellar aberration. These two factors will cause the difference between the actual measurement of spacecraft and the corresponding information in the ephemeris, and then affect the navigation accuracy. To solve this problem, a celestial navigation method considering relativistic effect was proposed in this paper. The star angle measurement model is correct by relativistic effect to conform to the actual observation result, so as to improve the navigation accuracy. The simulation result shows that the proposed method can effectively correct the influence of relativistic effect on spacecraft star angle navigation in Mars surrounding orbit. When the star sensor measurement error is 3″ and the Mars sensor measurement error is 0.05°, the corrected average position error and average velocity error are reduced by 13.97% and 13.89% respectively, compared with the uncorrected case.