The lighting design, construction and acceptance of road or tunnel are based on "The standard of ventilation and lighting design for highway tunnel" and "Outdoor Lighting Measurement Methods". Which determined the methods: measured the point set on the road line with the luminance meter from a small field angle. This method only concern a few measuring points, but not the surrounding environment, so, it cannot reflect the vehicle drivers actual visual experience. This paper takes the small target visibility visual indicator into road and tunnel lighting evaluation system. Based on luminance threshold contrast simulation model, it analysis the positive and negative luminance contrast conditions and fits out the relationship between the identification probability with relative contrast. By increasing the contrast, can increase its visibility, so as to create better conditions for road transport safety.