Abstract: To discuss the STBC practicability, the STBC performance in a frequency-selectivity fading channel is studied. A simulation model in the channel is developed using SIMULINK, which comprises a channel, transmitting end and receiving end, where the channel comprises a multipath Rayleigh channel and Gaussian white noise; the transmitting end comprises a serial-parallel converter and space-time block coder with spectrum spread and signals disturbed; the receiving end uses an ideal RAKE receiver. The simulating results showed that when a channel varies slowly the BER (bit error rate) falls down obviously and while it varies quickly the BER rises up somewhat, and either the falling or rising occurs with the increasing number of channel paths. And the more the number of paths is, the clearer the BER rises up.