Abstract: According to the fact of random task assignment widely existing in combat process, the paper utilizes the random service system and system engineering to research for combat system task planning method based on the mode of combat task assignment. The generalized combat system is abstracted into general command unit, reconnaissance unit, combat unit and target, etc. The single-level combat system organization structure decided by task assignment mode, operation rule, operation order and the target arrival rule is described. The combat system operational mechanism and effectiveness evaluation model during centralized assignment and autonomous assignment are demonstrated. Eventually, the application of evaluation model in army aviation air attack is expatiated with simulation.