Based on underground continuous mining technologies, it is one of the developing directions of modern underground metal mines to implement induction roof instability caving, which is used to handle mined-out area. And this mechanical instability process is a typical slow-speed time-varying boundary mechanical problem, of which the main characteristic is dynamic time-varying effect when inducing roof caving. To RFPA software, it's an effective way to deal with the problem of unit destruction by using the method of weakening unit nature and to simulate the time-varying boundary problem during caving properly and dynamically, obtaining time-varying effect when roof caving is induced. Using the RFPA software taking the T112-T115 mine of 92# orebody in Tongkeng Mine as the research object, the time-varying effect was simulated and analyzed during the induction roof caving. The results are showed as following: (1) The stable exposed area of mined-out area can be up to 4500m2. (2) The roof surrounding rock mass has been avianized seriously after the fourth ore section is stoped, and the caving line height is 48m. Thus the roof caving must be artificially induced after stoping the fourth ore section to make sure safe mining. The safe height of induction caving engineering must be up 50m. The results of time-varying effect show that the surrounding rock mass are avianized by the change of continuous stoping space. It is an effective method to tackle mined-out area by inducing roof instability caving through artificial disturbance in the partial roof.