A firepower assignment of army troop is established to meet the demands of informationization combat of army troop. The army troop could be divided into information unit, main combat unit, command unit and support unit based on the analysis of the organization and forming of army troop combat forces, and evaluation method of the operational effectiveness of each unit was presented, and the operation principle of army troop was determined according to the operational effectiveness evaluation. Result shows that optimized firepower assignment scheme could be obtained, and scheme is effective. It has been used in army troop combat simulation.