Abstract: The performance of STBC (space-time block code) in time-varying fading channel is studied with its practicability in focus. A simulation model in time-varying fading channel is developed using SIMULINK, which consists a channel, transmitting end and receiving end. Further, the channel comprises a multipath Rayleigh channel and Gaussian white noise, the transmitting end comprises signal source, serial-parallel converter, modulator, STBC and power dividing block and the receiving end comprises signal combiner, maximum likelihood decoder, modem and BER computing block. Simulating results indicated that in a flat and slowly fading channel the performance of STTD (space-time transmit diversity) is much better than it in single transmitting/receiving case and can be improved quickly with increasing SNR. But, if in a flat time-varying fading channel, the performance of STTD degrades with increasing maximum Doppler shift especially in case of high SNR.