The low embankment of the expressway is limited by the height of the subgrade, which easily causes problems such as excessive settlement or uneven settlement after construction. At present, the subgrade design and maintenance codes did not uniformly regulate the design of the low embankment, resulting in many problems that would affect the normal use of the project during the construction and operation of the low embankment. Based on the risk assessment theory of geological disaster, this paper analyzed some factors such as drying and wetting cycle and traffic load. In addition, considering the maintenance and repair, these factors were modified and the evaluation method of low-embankment-subgrade in service status was proposed. The method used fuzzy comprehensive evaluation method and matter-element analysis method to analyze the structural quality vulnerability in construction period, the risk of subgrade in operation period and the modified value of maintenance and repair. Finally, it obtained the comprehensive risk of low-embankment-subgrade. The method was applied to the project example of the low embankment in northern Zhejiang. The result shows that the comprehensive risk is low and the service state risk is basically consistent with the filed survey result, which illustrate the feasibility of the evaluation method.