The invention relates to a method and a system for improving a security rate of an MIMO security communication system. The method for improving the security rate of the MIMO security communication system is used for realizing the maximal security rate under the constraint of the maximal transmitting power of a transmitting terminal and the number of non-zero elements in an antenna sub-array matrix by using joint beamforming and antenna sub-array forming strategies, so that the relatively high security rate can be obtained under the condition of greatly reducing the cost of the system hardware.