The rock slopes with tunnels appear widely in the actual project, but there is no executable basis for the seismic stability calculation of the rock slope with tunnel. According to the upper bound theorem of plastic limit analysis and pseudostatic method, the upper bound solution of the safety factor of the rock slope with tunnel was rigorously derived under earthquake loading. This upper solution takes into account the design parameters of the slope and the tunnel, the horizontal and vertical seismic loads, and the physical and mechanical parameters of the rock mass. Comparing the calculated results with the existing results, the validity of the proposed method was verified. The sensitivity and influence of different parameters on the seismic stability of the slope were analyzed. The results show that the three factors such as the horizontal seismic force coefficient, the slope height, and the internal friction angle are the three key factors that influence the sensitivity of the safety factor and have a great effect on it.