Aimed at the problems of dynamic environment and unpredictable scene in unmanned aerial vehicle (UAV) autonomous search mission planning, the classical simple hierarchical ordered planner (SHOP) method is improved, and an iterative mission planning model with multiple planning and multiple execution is proposed based on the improved SHOP method. It provides a feasible solution to the mission planning problem with incomplete information. The simulation environment was built, taking the autonomous search task of UAV as an example, the feasibility and practicability of the iterative mission planning model were verified. Compared with the SHOP planning method, the advantages of the iterative planning method are illustrated.