Spatial variation and influencing factors of CEC of the soil in the Dagu River Basin were studied with geostatistical and multiple regression analysis methods. Results show that CEC of the soil in the upper and under layers displayed significant positive correlations with organic matter, clay and silt, and significant negative correlation with sand. The correlation coefficient was the biggest between CEC and clay, and the smallest between CEC and silt. In terms of contribution of the factors to CEC, they were in the order of clay > organic matter > sand, and the mean contribution of clay was 1.5~2.5 times as much as that of organic matter. The cokriging method, which used clay as instrumental variable, produced more accurate results than the ordinary kriging method, and reduced RMSE of the soils in the upper and under layers by 18.94% and 41.05%, respectively. Furthermore, the relationship between the secondary and the primary variables governed accuracy of the estimation. Soil CECs were higher in the middle east, northwest and middle southwest of the Dagu River Basin, but much lower in the north and southwest tip. Hence the two regions are critical ones for soil amelioration. The soil fertility therein can be improved by increasing application of organic manure and adopting other soil building practices.