When attacked by the Anti-Ship Missile (ASM) with infrared guidance function, the surface warship need to use Infrared Decoy(ID) and infrared guidance Ship-to-Air Missile (SAM) cooperatively in reaction, where firepower conflict must be avoided. Analysis is made to the cooperative combat situation of ID with SAM, based on which a firepower conflict model is established. Then the simulation method is adopted to detect whether the firepower conflict between ID and SAM is existed or not during the combat, and a strategy of conflict resolution is given. The calculation results prove the validity of the model and the method, which can improve the anti-missile effectiveness of surface warship when using soft and hard weapons cooperatively.