Dynamic Power Management(DPM) is a design methodology aiming at reducing power consumption of electronic systems by performing selective shutdown of idle system resources. How to improve predictive accuracy is the main problem needed to be solved in DPM policy based prediction. With the assumption of the relevancy among the pieces of idle time,the exponential average policy Under is prevalently used can not predict accurately when abnormal error like a sudden long or short idle period happens. In this paper, the authors propose a new adaptive DPM predictive policy basing on improved exponential average model and mathematic definition of abnormal error. The policy would self-adjust to get higher predictive accuracy if sudden error occurs. The new policy excels the existed ones in prediction accuracy.