Drivers' visual adaptation influenced traffic safty. In order to consider drivers' visual adaptation directly when determine road tunnel threshold zone luminance, drives' pupil size data were measured when they driving into tunnels, and established a mathematical model to describe the relationship between the max speeds of drivers' pupil area changes and related parameters. The maximum speed of drivers' pupil size changes, which could ensure drivers' visual function, were confirmed as critical speeds. The minimum tunnel threshold zone luminance was calculated based on the critical speeds, the relationship between the minimum tunnel threshold zone luminance and corresponding access zone luminance were analyzed, a mathematical model was established to describe the relationship between tunnel threshold zone luminance and access zone luminance with regression method, tunnel threshold zone luminance determined method was proposed based on drivers' visual adaptation.