The invention discloses a variable speed-limit control method of congested upper streams of a snowy expressway. A plurality of traffic flow detectors are arranged on the expressway in an equidistant mode, the congested condition of each section of the expressway is judged based on traffic flow data, acquired through real-time and automatic detection, of each section of the expressway, spreading characteristics of congestion waves are used for calculation to select the optimum speed-limit value of the congested-section upper streams of the snowy expressway, the current speed-limit value is displayed in real time through a road-side variable speed-limit information prompting plate, and therefore the speed of running on the expressway under snowy conditions can be dynamically controlled. The variable speed-limit control method has important significance in reducing rear-end collisions happened when the upper streams of congested sections in snowy days are congested and improving running safety on the expressway in adverse weather.