Abstract: In this paper, the mission orbit design and analysis of a potential extended mission, Phobos close approach exploration, was carried out. The state at the end of the main mission was used as the input of the extended mission in this paper. Through analysis, it was concluded that Mars perturbation force could be used to adjust the argument of perigee, and the intersection frequency was related to the value of semi-major axis and eccentricity. Orbit descent maneuver should be performed to increase the number of intersections. As a result, the possibility of conducting aero-braking in order to reduce fuel consumption was analyzed. Finally, phase adjustment maneuver was calculated to complete the Phobos close approach exploration mission. The orbit design results and the velocity increment are given by simulation. The results of this paper can provide reference for orbit design of Tianwen-1 orbiter’s extended missions.