In order to analyze the stability of the slope at the entrance of the tunnel, the upper-bound limit analysis method is used in this paper to study the influence of the crack on the overall stability of the slope under seismic force and the distribution of the crack position. A formula for calculating the stability number reflecting the critical slope height is derived, and a method for calculating the safety factor of the slope indirectly by means of the stability chart is given by an example. The results indicated that the larger the slope angle, seismic coefficient and the depth of crack is, the smaller the stability number will be, and with the increase of the depth coefficient of tunnel, the higher the stability number will be. The increase of crack depth leads to the distribution of crack location closer to the edge of the slope, while the increase of seismic coefficient and slope angle leads to the distribution of crack location farther away from the edge of the slope. As the seismic and crack depth becomes larger, the safety factor of the slope decreases, which is not conducive to the slope stability.