Abstract: Some remarkable anormalies of precursory observation appeared in Yunnan area before Wenchuan earthquake. According to the seismogenic scale, we think these anormalies may have a close relationship with Wenchuan M_S8.0 and realized that remarkable extremum anormalies maybe the precursor of big earthquakes with M_S≥7.0. Some researcher think it is a common character that no or few precursory anormalies appeared in epicentral area, so did the Wenchuan M_S8.0 earthquake. The beginning and ending time of anormalies were various, and the distribution of anormalies was complex. So it was difficult to predict the Wenchuan M_S8.0 earthquake using the common characters summarized after the earthquake.