To study the influence of the initial gap of the shear key on the isolation performance of friction pendulum bearings, the isolation models with different gaps are established, and the nonlinear time history analysis under different PGA earthquakes is carried out, and compared with the non-isolation model. The results show that the initial gap of the shear key affects the operating mode and isolation efficiency of the friction pendulum bearing under frequent earthquakes, but does not affect the isolation efficiency of the design and rare earthquakes. Meanwhile, the gap affects the failure time of the shear key under the design earthquake. The model responses of different gap values tend to be consistent after all shear keys fail.