Abstract: As well known, Multiple-Input Multiple-Output (MIMO) technique can be used in conjunction with scheduling to further increase the throughput of the multiuser system. This study analyzes the expected throughput of the multiuser downlink scheduling system based on block diagonalization zero-forcing transmission strategy. We present four theorems to describe the correlation between any two users' mutual information in the system and give three estimations including one close-form approximation of the throughput of the system. It turns out that the multiuser diversity gain is significant when the number of antennas becomes large.