With the widespread application of power line carrier communication, broadband multi-input multi-output (MIMO) system will have a co-channel interference which is the largest factor influencing the MIMO system of broadband power line carrier in addition to asynchronous pulse noise and pulse cycle. Aiming at this problem, this paper, by using multiple input multiple output channel state information, the sender with the method of block diagonalization, eliminates the interference between the channel, so as to improve the capacity of broadband power line carrier system, at the same time reduces the bit error rate of the system. Through the simulation results and analysis can show that the proposed block diagonalization precoding method effectively eliminates the common channel interference, improves the drying ratio, thus enhances the maximum mutual information of the system and reduces the bit error performance of the system.