Based on the previous studies,a new mathematical model is established, which is suitable for probabilistic method of predicting seismic intensity in key monitoring area. The sensitivities of the factors affecting prediction to the results are analysed.It is found that the intensity attenuation law plays an even more important role in bringing about the uncertainty. In the light of the principle of uncertainty correction for normal distribution function in seismic hazard analysis, an improved method to correct the uncertainty in intensity prediction is demonstrated and is applied in Hexi key monitoring area. Seismicity period and magnitude interval are taken into account to determine the magnitude-frequency relation. Therefore,the relation secured in this paper may be more accurate.