The CAPPS(City Air Pollution Prediction System) was used to simulate the air pollutant index of the primary air pollutants(SO₂ NO_x TSP) in Shijiazhuang City . The results show that the modification of time coefficient of pollutant emission ( T_i) and the experiential coefficient (K_i) should be added when it being used. It also needed to modify with the percent of raising dust (F) to the CAPPS in the cities of North China. The correlation coefficients between the predictions and the observations of SO₂ , NO_x and TSP were raised to 0.951 , 0.854 and 0.880 respectively after modifications by T_iK_i and F.