The invention discloses a continuous monitoring system for flue gas pollutants. The system is used for monitoring contents of elementary mercury, mercury ions and total mercury in flue gas. By arrangement of a sampling channel and a detection system, the influence of adsorbent particles of a particle filter in the channel on a detection result can be reduced. The continuous monitoring system for the flue gas pollutants can be applied to precisely continuous monitoring for mercury discharging of a fixed pollution source such as a chemical plant, a coal-fired power plant and a waste treatment plant, so as to realize discharge control over the pollution source and provide real-time and reliable data for environmental monitoring and environmental protection.