The earthquakes, which occurred in Haiyuan, Tangshan and Wenchuan, have caused serious damages in the loess area and the abnormal intensity sites are commonly found during the earthquakes. The investigation of the actual earthquake damages and character analysis on sites shows that the topography, loess overburden and underground water level and many other factors afect the intensity. In this paper, the thickness of loess overburden of Tianshui City is achieved by inversion algorithm based on site exploration and microtremor test; the amplification efect of peak ground motion acceleration is calculated using numerical method; a complete formula is obtained through summarizing previous achievements and is used to calculate the abnormal intensity under the multifactorial influence. Finally, a seismic intensity anomaly distribution map is plotted applying the graphic information system(GIS) software in Maiji District, Tianshui City. Through the practical investigation of earthquake disaster, it is found that the figure fits the distribution of actual intensity anomaly very well. The earthquakes, which occurred in Haiyuan, Tangshan and Wenchuan, have caused serious damages in the loess area and the abnormal intensity sites are commonly found during the earthquakes. The investigation of the actual earthquake damages and character analysis on sites shows that the topography, loess overburden and underground water level and many other factors afect the intensity. In this paper, the thickness of loess overburden of Tianshui City is achieved by inversion algorithm based on site exploration and microtremor test; the amplification efect of peak ground motion acceleration is calculated using numerical method; a complete formula is obtained through summarizing previous achievements and is used to calculate the abnormal intensity under the multifactorial influence. Finally, a seismic intensity anomaly distribution map is plotted applying the graphic information system (GIS) software in Maiji District, Tianshui City. Through the practical investigation of earthquake disast er, it is found that the figure fits the distribution of actual intensity anomaly very well.