Studies show that driving in foggy environment is a security risk, and when driving in foggy environment, the drivers are easy to accelerate unconsciously. The safety information prompted to the driver is mainly from fog lights, road warning signs and the traffic radio. In order to increase the quality of the safety tips to prevent drivers from unintended acceleration and ensure the security of driving in foggy environment, the study proposes a safety speed assessment method for driving in foggy environment, combining the information of driving environment, vehicle’s speed and the multimedia system.The method uses camera which is installed on the front windshield pillar to collect the image about the environment, and uses the dark channel prior theory to calculate the visibility. And by using the environment visibility, the safety speed can be calculated based on the kinematics theory. And it is appropriate for vehicles which have different braking performance. If the vehicle speed is faster than the safety value, the system will alert the driver to pay attention to the current speed.The method is verified by the semi-physical simulation. The results show that the method can effectively prompt the safety speed to ensure the safety of driving in 50-300m low visibility environment. Especially when the visibility is about 50m, the system can warning validly and drivers can make vehicle speed in a safety range, which is helpful for the traffic safety. If combined with the vehicle network, it would greatly improve the accuracy.