The invention discloses a low-complexity adaptive transmission multi-antenna transmission method and a low-complexity adaptive transmission multi-antenna transmission system. The method comprises the following steps of: constructing equivalent channels according to the acquired channel information and formula shown in the specification; calculating signal-to-interface-and-noise ratio after single-flow detection from an equivalent channel matrix; selecting MCS according to a throughput maximization principle; encoding and modulating a transmitted symbol by a transmitting end according to the selected MCS; performing space time processing by using a determined encoding mode and then transmitting the symbol from different physical antennas; receiving the symbol transmitted by the transmitting end by the receiving end; constructing the equivalent channel matrix through which the symbol passes through an equivalent channel matrix construction formula by actual channel estimation; performing Minimum Mean Square Error (MMSE) linear detection by using the equivalent channel matrix; and finally finishing the process of demodulation and decoding. The low-complexity adaptive transmission multi-antenna transmission method and system detect the optimal coding by using MMSE constructed by Clifford complete orthogonal basis, has simple diffusion matrix elements selected from {0, +-1, +-j}, and effectively reduce the calculation complexity for performing the adaptive transmission with the multi-antenna system by using the single-channel encoder for transmission.