Abstract： Based on the underground structure scheme of large houses of a hydro-electrical project，over hundred working conditions are numerically simulated. The variation law of displacement of house periphery is studied with considering four basic classes of rock masses，four different depths and different lateral initial stresses. As a stability criterion，the specific value of displacement of rock masses is presented to judge whether the long prestressed cables are needed to reinforce the rock masses. It is mentioned that a loosen-cracking zone of the side wall should be considered in many conditions，so that the numerical analysis result will be more closed to the reality. Finally，a simulating computation is made for a project. The computed displacement shows a good agreement to the monitoring result.
