Drivers' adaptation luminance changes with the changing of the sense within their visual field when they drive into tunnels. Tunnel lighting design should provide brightness levels in accord with drivers' visual adaptation; so, it is necessary to find out drivers' adaptation luminance changing rule when driving into tunnels. For this purpose, we took four tunnels as the research objects, and measured and calculated drivers' adaptation luminance at different positions within a stopping sight distance to the tunnel entrances. The results indicate that drivers' adaptation luminance changing rule is similar when they drive into the same tunnel at different time. Drivers' adaptation luminance decreases gradually when they drive into tunnels, but the decrease is nonlinear, and drivers' adaptation luminance decreases fast when they are in the distance of 20 m to30 m from the entrance of a tunnel.