Taking the slope at the East Open Pit Mine of Pingshuo Coal Industry Co. where two soil landslides occurred successively as the research background, in consideration of the current situation that valid data lacks and relatively large error exists in experience evaluation, data of geological survey points in interfaces between rock and soil layers were fully used and the drilling data range was effectively expanded to provide valid data for high-precision interface fitting. A Closest Point algorithm-based structural analysis model was applied to conduct Kriging interpolation calculations, which made the two algorithms coupled. Thus a three-dimensional fitting model of all rock and soil layers can be completed. By comparing the data of measuring points selected from the field, the accuracy of the interface fitting method is much higher than the traditional method of human experience.