The invention discloses a multi-antenna transportation communication network system and a signal detection method. The multi-antenna transportation communication network system comprises a transmitting end and a receiving end. A spatial multiplexing technique of a multiple-input multiple-output system is adopted for the transmitting end, and a plurality of transmitting antennas are mounted on vehicular nodes or roadside nodes, so that transportation communication signals can be transmitted by the aid of MIMO (multiple-input multiple-output) channels; according the receiving end, a plurality of receiving antennas are mounted on the vehicular nodes or roadside nodes for receiving signals, and the signals which are received on the various antennas are combined with one another, so that the signals can be jointly detected. The signal detection method includes modeling transportation communication channels at the receiving end by the aid of a basis expansion model, and estimating basis coefficients on the basis of channel models by the aid of a channel estimation process to obtain channel information; detecting the signals according to the obtained channel information by the aid of a sphere detection process. The multi-antenna transportation communication network system and the signal detection method have the advantages that transmission bit error rates of transportation communication networks can be effectively reduced, and the complexity can be effectively lowered.