In order to reasonably determine the safe speed limit of expressway under several meteorological conditions such as stagnant water, icing, snow, fog, and provide the driver with the maximum acceptable safe speed, this paper proposes a Freeway variable speed limit system based on traffic meteorological environment monitoring. This paper establishes a speed limit model based on visibility, illumination and road surface state. The STM32f103 is proposed as a controller to collect meteorological information in real time using road surface condition monitoring equipment, visibility meter and illumination meter. And use LED information board to prompt the maximum safe speed in real time. This paper is based on QT5 development of the host computer client. QT has the advantages of high modularity and good reusability, and can be extended to other functions as needed. ? 2019 SPIE.