Stability against deep sliding of gravity dam design has been a key issue. In natural rock of many engineerings, there are often weak structure planes, gently - dipping fissures and faults in the dam foundation rock. The combination of these unsafely structural surfaces may constitute a continuous or discontinuous slip surface in the dam foundation, thus, brings a serious threat to the deep sliding stability of dam. In order to provide the basis for optimization scheme of foundation treatment, and to verify numerical analysis, we use geomechanical model test technique to study deep sliding stability of the spillway section of Tingzikou Dam. There were two programs with processing and without processing. On the basis of operating conditions of the dam, the displacement fields and law of the key parts in dam and foundation were analyzed, and the displacement development law, failure mechanism, sliding path and anti - slide safety factor under the overload were observed. Safety evaluation for deep anti - slide stability and reinforcement treatment measures for Tingzikou Dam foundation before and after treatment were made.