The top rock of exit of the diversion tunnel for turbines and the slope of Geheyan Hydropower Plant is limestone, and the underlying rock is shale. The monitoring data obtained by bore hole inclinometers arranged at the shale position showed that the direction of displacement of earth surface of slope is always toward the inside of mountain, and it isn't as usual toward the outside of mountain. This abnormal phenomenon once was a puzzling problem. For solving this problem, the method of pipeconfigurationline analysis was employed, and a satisfactory explanation was obtained at last. A brief introduction to the definition of pipe configuration line, the method of pipeconfigurationline analysis and how to use the method for solving the problems of displacement of slope is done.