Weapon equipment system-of-systems(WESoS) capability planning is an important part of the WESoS research area. Taking the time span and cost of capability planning as the optimization objectives, the multi-objective optimization model of WESoS capability planning is proposed. At the base of WESoS capability spaces description, the method of modeling WESoS capability planning is presented. Genetic algorithm is employed to solve the optimization problem. Then the quantitative method of capability gap analysis is presented as well. The proposed approach provides groundwork in certain degree for quantitative analysis of WESoS capability. Finally, a numerical example is given to illustrate the reasonability of the proposed approach.