Directed against the demarcating problems of deep tunnel and shallow tunnel in exiting methods, the paper indicates the demarcating method from the viewpoint of characteristic of surrounding rock pressure according to the results of field observation and numerical simulation. By use of numerical simulation technique, the paper,for the first time, expounds the demarcating thought which is based on the changing law of soil lateral pressure coefficient in the centerline. The method is proved feasible by two engineering cases, and is of importantce to lining design and construction of soil tunnel.