Abstract: A large number of unstable rock masses are distributed in the southwestern region of China, and they are extremely prone to collapse disasters under the action of earthquakes. Through large-scale shaking table model tests, the instability failure modes and ground motion acceleration responses under different earthquake wave loading directions and different loading amplitudes under strong earthquake conditions were studied. Moreover, the theoretical formula for the critical deflection angle of collapse instability and the method verification were proposed.The test results show that: When the earthquake wave loading direction is X, the failure mode is mainly toppling failure. When the earthquake wave loading direction is XZ, the failure mode is mainly a mixed failure of sliding and toppling. The acceleration response characteristics of the two earthquake wave loading directions are as follows: With the increase of the slope elevation, the PGA amplification factors in both directions increase significantly, and the trends of the PGA amplification factor curves of the two are basically the same. However, the amplification factor value in the X loading direction is greater than that in the XZ loading direction. When the loading direction is the same, the larger the loading amplitude, the greater the PGA amplification factor. Different earthquake wave loading directions will lead to different failure modes and also cause slightly different critical deflection angles. The theoretical calculation shows that the critical deflection angle for toppling failure is 34.28°. The critical deflection angle for the mixed failure of sliding and toppling needs to be calculated according to the horizontal displacement and vertical displacement of movement. The analysis results are in good agreement with the test phenomena, further revealing the influence of different loading directions and amplitudes on the instability failure mode and ground motion acceleration response of unstable rock masses under strong earthquake action.