In this work, the theory of the coseismic displacement field is first considered in the aseismic design of tunnels. We estimate earthquake dislocation in the engineering area by collecting historical earthquake rupture data. The coseismic displacement field around the tunnel is calculated through the splitting nodes method and applied in combination with the pseudostatic method in the aseismic design of a highway tunnel in Yunnan Province. Results show that the method based on coseismic displacement for the aseismic design of tunnels can provide a powerful quantitative analytical tool for the estimation of possible future earthquake disasters. If the natural vibration period and bedrock response spectrum are unknown, the coseismic displacement field can be used to estimate the far-field shear strain when conducting the quasistatic aseismic design of the tunnel. The forced displacement of the north and south segments of a tunnel in Yunnan is approximately 6 cm if earthquakes occur along the Longling-Lancang Fault Zone. If earthquakes occur along the Longling-Ruili Fault, forced displacement will cause reverse movement in the north and south parts of the tunnel. These movements will exert a pronounced shear effect on the middle of the tunnel, and lateral and vertical differential movements in the tunnel will intensify.