Aiming at the problem of automatic planning for agile imaging satellite, the architecture of automatic planning combined with planning, decision making and information feedback was presented. The architecture, components and functions of automatic planning were introduced. The model based on constraint network on timelines was constructed according to the satellite physical constrains and operational constrains. The activity sequences were constructed through connecting various activities. And a heuristic algorithm based on activity sequences was presented. The algorithm was composed of two parts: planning and decision making. The algorithm could plan based on heuristic rules when satellite was performing every activity sequence, and make decision when the activity sequence was completed. Finally, satisfactory results are obtained through experiments, which show that the architecture of automatic planning and the model are reasonable, and the algorithm is efficient.