To guarantee the construction safety and traffic safety in the process of freeway reconstruction and extension, the setting of speed limit signs at the upstream of reconstruction and extension work zone was studied. Based on the analysis of the visual characteristics and braking characteristics of drivers in the process of driving in daytime and nighttime, the model of driver’s visual distance and the model of advance distance of speed limit sign were built, and a method for calculating the spacing of gradient speed limit signs at the upstream of work zone was proposed, which was then applied to the reconstruction and extension work zone in Jilin to Longjia Airport section of Huiwu Freeway. In the end, based on kinematics calculation method, the vehicle mean deceleration characteristics between different speed limit signs were obtained. Results show that with the increase of the values of speed limit, the spacing of adjacent speed limit signs in daytime and nighttime increased, which were positively linear correlated, and the spacing of speed limit signs in nighttime was greater than that in daytime. With the decrease of the values of speed limit, the mean deceleration of the vehicle in daytime and nighttime decreased, which were approximately in a positive linear correlation, and the mean deceleration in nighttime was less than that in daytime. The setting of spacing accorded with the psychological and physiological characteristics of drivers during the process of driving deceleration, which proves the rationality of the proposed calculation model for spacing.