An earthquake preparation physical model was established based on observation data of sand layer stress instrument in Changping and Xiji, Beijing, earthquake precursor in the past 30 years observed by this instrument and precursor of Indonesia Earthquake (M =8.7) on December 26, 2004.The short-term and impending precursor of Wenchuan Earthquake recorded by the sand layer stress instrument was in accordance with this model.The observed short-term and impending abnormal stage change of time and shape appeared in March,2008, which was in accordance with the observation results of satellite thermal infrared and other testing methods in the aspect of time, had very obvious characters of impending earthquake anomaly.