A new model changes detecting method in fast fading channel structure was proposed.The new method aimed at the amplitude of the signal to detect the sample time points that channel suddenly changed.It educed the theoretic expression of model changes detecting method in fast fading channel by dynamic programming (DP) algorithm

and constructed the principle of vary structure channel model switching.The result of theoretic analysis and simulation experiment show that the method can detect the sample time points of model changes effectually by detecting the amplitude of the signal

and switch the channel model in these time points to approach a good estimator precision.