The invention discloses a signal processing method, a system and a device of a multi-antenna system, which are applied to a wireless network system which includes a transmitting end and a receiving end; the method comprises the following steps: the transmitting end expands real and imaginary parts of a modulation signal to obtain a real number transmission column vector which is equivalent to themodulation signal, and a generator matrix is constructed by the quantity of transmitting antennas and the transmission rate; the transmitting end obtains a space-time coding matrix according to the real number transmission column vector and the generator matrix, and then the pace-time coding matrix is transmitted to the receiving end by multiple antennas; in addition, the receiving end expands the real and imaginary parts of a receiving symbol from the transmitting end, so as to obtain the equivalent real number receiving column vector, a generator matrix is constructed by the quantity of transmitting antennas and the transmission rate, and a real number equivalent information channel matrix is further obtained, so as to detect the real number transmission column vector; the invention canutilize an uniform transmission mode to switch different transmission modes, so as to reduce storage requirements and operation complexity of transceiving equipment.