A resource allocation method for MIMO (multi-input multi-output-OFDM (orthogonal frequency-division multiplex) of multi-user access systems includes A) for each sub-carrier or group of sub-carriers of OFDM, grouping signature vectors of users at a time period according to correlations of the signature vectors; B) from the grouping results, selecting the signature vectors according to a scheduling rule; assigning the sub-carrier frequency and time resource to users of which simultaneously the selected signature vectors have low correlations; and assigning spatial resource to the users corresponding to the selected signature vectors. By minimizing the spatial co-channel interference to an acceptable low level, the complexity significantly in the joint multi-user optimization is reduced.