Abstract: The optimum channel capacity for using diversity technique in the Nakagami fading or Weibull fading channels has been derived based on the optimum capacity of multi-antenna Gaussian channel model. The numerical simulation results show that channel capacity will be affected by fading severity and diversity performance. For the same SNR, two kinds of fading channel capacity increase as the fading severity increases. Moreover, the fading severity affects the channel capacity more on the Weibull fading channel capacity than on Nakagami fading channel. For the same fading severity and the same SNR, the optimum capacity of the channel with selective diversity is higher than that without selective diversity. Optimized switch threshold is obtained in the Weibull fading channel by using switch stay combining technology.