Abstract: The change behavior of inner rock mass for combined mining on the basis of analysis of numerical value and actual deformation is explored. Because of effect under combined underground and open pit mining, mechanism about superimposition of deformation and change behavior depends on respectively amount of both mining methods. Deformation of rock mass would more present behavior of underground mining as slope dip angle is small. Therefore, under influence of the same amount in underground excavation, the range and depth of slope deformation are increased as slope dip angle is increased. Both amount of excavation directly influences quantity value and direction of vector. Change of each amount of excavation would make the different behavior of failure and moving mechanism for rock mass is produced.