Considering the low spectrum resource utilization restricting highspeed data transmission over fading channels, this paper proposes an adaptive Turbocoded modulation to maximize the spectral efficiency of system. Fading channel is divided into N adjacent regions, and Lagrange Multiplier is used to obtain the optimal switching thresholds under an average power constraint and biterror constraint. Numerical results show that the spectral efficiency of adaptive Turbocoded modulation has a 2～3 dB gain in performance with the same complexity of TCM scheme, and within 3 dB of the fading Shannon limit; comparing with the not optimized 4 fading regions and the optimal 4 fading regions, nearly 1 dB performance gain can be obtained. The average spectral efficiency of wireless communication system can improve significantly.