Abstract: Serious traffic accident such as hundreds of vehicles rear-end collision often occurs under fog weather, so it is important to evaluate fog risk for traffic safety. Based on fog frequency, fog duration and visibility, fog hazard index (FHI) is suggested in this paper, and normalized fog hazard index (NFHI) calculation method was established, which is suitable for Chinese meteorological standard. NFHI was modified for suitable to numerical forecast products of fog, then the new index was brought forward. According to fog observational data from five stations along Jingjintang expressway in recent 36 years, fog risk grades in four seasons were determined in terms of new index. NFHI at different sites was calculated by numerical forecast results. This index can also be used to select the optimum route by risk comparison of different paths, which can provide scientific reference for traffic safety.