A new method of antenna aperture sharing for communication and radar system is presented on the basis of the sparse array antenna and staggered sub-array theory. An analysis is made to the key indicators of the radar and communications with a shared aperture. Two key indicators are chosen as optimization objectives: the maximum peak side-lobe level of the radar array pattern, and the communication channel capacity of Multiple-Input Multiple-Output (MIMO) communication system. The array element position optimization problem under given array element number and aperture size is put forward. After setting a preference degree, the optimization problem is transformed into a single-objective optimization problem, and a solving method based on genetic algorithm is given. Simulations and analysis prove the feasibility of the proposed optimization method, and the optimization curves for different preference degrees are given.(2015JM6306);武警工程大学基础研究项目(WJ20160132)