The resource allocation algorithm in multi-user multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) systems has been studied. The user's fairness is ensured in this algorithm, and based on minimum transmitting power to allocate the sub-carriers and the bits in system. The sub-carriers' first allocation is done according to the user's channel gain under the order from worst to best. And then, by comparing their powers to find the most suitable sub-carriers ultimately. Finally, the greedy water-filling algorithm is used to allocate bits for the sub-carrier. Simulation results have shown that the transmitting power can be decreased and the system performance has been improved.