The invention discloses an expressway agglomerate fog real-time monitoring system and method based on a GIS system. The system comprises the GIS system arranged in a computer, a plurality of cameras arranged on an expressway, a plurality of weather stations, a plurality of environment monitoring stations and a display screen. The GIS system is provided with an image identification module. Each camera is connected with a closest weather station and environment monitoring station and then is connected with an input end of the GIS system. The display screen is connected with an output end of the GIS system. According to the invention, the existing expressway camera data, free haze data of the environment monitoring stations and weather data of the weather stations are fully utilized, a space analysis technology of the GIS system is combined, and haze, fog and agglomerate fog are effectively distinguished and monitored; in addition, no other hardware equipment is arranged except the computer system of the GIS system and the display screen, and the cost is low.