Using the extreme value theory, b-value conforming to Gubmel distribution is caculated to replace normal b-value method,which needs higher quality data. According to the phenomenon that seismicity diverging Poisson distribution before moderate-strong earthquake, Pois- son distribution coincident degree Yn-value is given. The new parameters then are applied in Yinchuan-Hetao and Qilian Mt. -Liupan Mt. seismic belts for prediction test. The result shows that the b-value and Yn-value are correlated well with moderate-strong earthquakes.