Abstract: In this paper, a new nonlinear nonsteady method for signal treatment is introduced in detail, which is valid and predominant. It is used to analysed the seismic wave.The EMD method and its process are presented through a great amount of data study. A range of good-shift of data is given from a lot of data analysis and the rule is given. When the frequency of combined sine wave is constant, the value of A2/A1 is very small, and it is over a limit; or the value of A2/A1 is large, and it is over a limit, EMD method is not applicable. When amplitude ratio of sine wave A2/A1 is constant, but the frequency varies, if the value of f2/f1 is very small, and it is over a limit; or the value of f2 is very close to f1, and the ratio f2/f1 is over a limit, the value of y is not able to be shifted by EMD method.