Abstract: Aiming at the measuring method of similarity search in time series，a similarity measuring method based on slope departure is proposed in this paper.To dispose the time series data with high dimension，multi-property，noise and default，a similarity measuring method is used to caculate the slope departure based on PLR solving the localization of slope distance measurement.In fact，the physical concept of this method proves more clearly and nicely.The maturity and the continuity of slope departure are proved.The example shows its validity.