The choice of portal elevation and gradient of upward slope values are critical to the safety and stability of the whole traffic line, especially, in the tunnel and bridge coupling process. To explore the dynamic response of tunnel portal section and upward slope under the influence of portal elevation and gradient of upward slope, models with different slope gradients and different portal elevations were constructed. These models were based on 3D numerical simulation, with the incident direction of seismic wave being parallel to the direction of the tunnel axis. Our results demonstrate that (1) Under seismic loads, with increasing distance from the tunnel portal, the displacement of the tunnel vault is gradually reduced, with the peak value of displacement located in the vault section of y=0 m (distance from the portal). Therefore, it is the portal section that is the most dangerous under the earthquake action, and it should receive the most attention when designing the whole tunnel line. (2) In this paper, Δ_max is defined as the maximum displacement difference of the tunnel section. The change rule of Δ_max indicates that with the increase of the gradient of upward slope, the portal elevation of tunnel should also be higher. The Δ_max defined in this study may provide a new method to evaluate the seismic dynamic response. (3) By setting the contrast model, which is pure slope without tunnel, the influence of tunnel on the dynamic response of slope is studied. Firstly, the peak value of slope displacement is smaller than that with tunnel. Secondly, with increasing portal elevation, the tunnel will influence the dynamic response of the slope surface, due to the effects of portal elevation and slope gradient.