Abstract: Statistical properties of the instantaneous distortion index in Motycka method are obtained. Some improvements of Motycka method of predicting the maximum expected instantaneous distortion index are given. A way of predicting the most probable peak instantaneous distortion in a long estimating period duration is presented and the accuracy of the estimation is described. Moreover, factors effecting the accuracy of predicting the most probable peak instantaneous distortion are discussed. Results show that the computing time of the present method is much less than that of Motycka method with about the same degree of accuracy in estimation.