The invention provides a signal detection method which comprises the following steps: a transmitting device converts signals needed for transmission into a plurality of symbol subflows the number of which is the same with that of transmitting antennas; the symbol subflows are respectively modulated; modulated results are respectively coded differentially; space-time code matrixes are constructed by utilization of differential coding symbols and respectively transmitted in continuous moments through the transmitting antennas; a receiving device receives the space-time code matrixes which are transmitted by the transmitting device, and signals after filtration are obtained by filtering the space-time code matrixes; the signals after filtration are judged differentially, and symbols which are generated by modulation of the transmitting device are obtained; after demodulation of the symbols, the symbol subflows which are transmitted by the transmitting device are obtained and then converted into signals which are transmitted by the transmitting device. Channels are unnecessary to estimate through the signal detection method and a signal detection system which are provided by an embodiment of the invention, thereby broadband resources are effectively saved.