The multi-objective optimization method is adopted to study the modeling of Weapon-Target Assignment (WTA) in ground target attacking.Firstlybased on the analysis to the characteristics of the ground target attackinga multi-objective optimization mathematical model is established.The optimization objectives are defined as the minimum risk of aircraft in penetration and the maximum target damage efficiencyand a quantitative method for evaluating the threat of air defense fire power to the aircraft is proposed based on grid map.Thenthe Non-dominated Sorted Genetic Algorithm-Ⅱ(NSGA-Ⅱ) is adopted to solve the problemand the components of the algorithm are designed.Finallya simulation example is built for experimental analysis.The simulation results show that the model and method in this paper can effectively solve WTA problem of ground target attackingwhich provides a reference for engineering implementation.