In order to improve the observation efficiency of intelligent remote sensing satellites and give full play to the application value of satellites, this paper proposed a new two-stage on-orbit mission planning model. The earth observation targets are divided into two types: fixed targets and user targets. This ensures that whereas dynamically and timely responding to the user targets, the utilization efficiency of satellite resources can be improved as much as possible, and provides a reference for judging whether the satellites are operating well. On this basis, this paper designs a two-stage on-orbit dynamic task planning scheme, which uses a greedy algorithm and a greedy algorithm based on heuristic rule to solve the fixed target stage and the user target stage. At the end of the article, a simulation test is carried out on the method of this paper, and the two-stage planning scheme is compared with the method of individual user target planning. The results proves that the method in this paper can achieve the priority planning of user goals, and verify the feasibility of the method in this paper.