Abstract: A trace-orthogonal space-time coding with full diversity and suitable for multi-user MIM0 transmission system is proposed. Through the introduction of this coding, it can make the system achieve full diversity which could ensure better BER when the signal to noise rate is higher. By changing the structure of the encoding matrices, the transmission rate of the user could be changed together. The MMSE decoder can be used in the system with low complexity compared with ML decoder.