Aiming at the problem of difficult task allocation of unmanned combat system composed of heterogeneous multi unmanned platforms, a mathematical model of task allocation is constructed. The operational scenarios and capabilities of the system are analyzed; The mathematical definitions are given from the aspects of target, mission, UAV and battlefield environment, and the corresponding mathematical model functions are given; The optimization objective function and constraint conditions of the system task allocation are given, and the particle swarm optimization algorithm is used to solve the example based on the task allocation model. The calculation results verify the rationality of the allocation model.