A novel low complexity user selection strategy was proposed for MIMO broadcast channels, where zero-forcing beamforming was considered. As the number of simultaneously supportable users at the same frequency is limited by the number of transmit and receive antennas, the base station may select a subset of users in a cell to serve. Exhaustive search for the optimal user set, however, is computationally prohibitive. We proposed a new sub-optimal user selection algorithm using the revised distance metric between subspaces spanned by the vectors of userspsila channels. Simulation results show that this new algorithm performs very close to the capacity-based algorithm with much lower computational complexity.