Level of Service of Safety is a new concept in the field of traffic safety in China and developed countries, it is a quality indicator which is used to describe the road traffic safety situation and roads providing service of traffic safety for traffic participants. Introducing the study status of the Level of Service of Safety in China and developed countries, the definition of the concept, applications and content. In order to objectively evaluate traffic safety performance at low-grade roads, the concept of the level of service of safety for low-grade roads is brought forward, the factors influencing the sections of level of service of safety are analyzed , then linear, the risk of the roadside, traffic volume, the proportion of trucks and 85% speed difference between cars and large vehicles are selected as the evaluations, level of service of safety for the basic sections of low-grade highway is divided into four levels, the grey class whitening function is established to determine the appropriate threshold, Grey Clustering Method is used to evaluate the level of service of safety for low-grade highway sections, and reasonability of the method is validated. The Grey Clustering Method is applied to evaluate traffic safety of actual low-grade highway section, the result shows that the proposed method is reasonable and feasible.