The invention provides a RUMSWF based low-complexity reduced rank balancing method in an MIMO system, which is improved from an MSWF based self-adapting reduced rank linear balancing method and is a reduced rank self-adapting MIMO linear balancing method which realizes a multilevel Weiner filter based on a rectangular block matrix and by a related subtraction structure. By improving the block matrix of the unitary multilevel Weiner filter, a rectangular matrix block of the square block matrix is selected as the block matrix, and the number of dimension of a received signal is reduced step by step in the forward recursive decomposition of the unitary multilevel Weiner filter, thereby reducing the iteration complexity of the self-adapting balancing and simultaneously increasing the convergence rate. The theoretical analysis and simulation result show that the low-complexity quick reduced rank self-adapting balancing method has the advantages of low complexity and quick convergence rate.In a V-BLAST system provided with 4 transmitting antennas and 8 receiving antennas and adopting the BPSK modulation, by only utilizing one half of complexity of the multilevel Weiner filter based balancing method, the error code performance which is only 0.78 dB lower than that of the multilevel Weiner filter based balancing method can be achieved.