In order to study the impact of decreasing illumination on distances cognition in dusk, real road experiments are performed. A certain quantity of randomly selected drivers perceives absolute space distances and relative ones in different environment illumination and depth distance in the real road. The cognition values, acquire distribution mode and character values are analyzed by using the statistical method. A mathematic model of cognition is built by regression and the cognition quantitative differences between day and dusk are compared. The results show that the cognitive values continuously augment with the environment illumination decreasing and there is a cubic expression relation between them. And the distance cognition value in dusk is larger than that in day under the same depth distance.