The invention discloses a monitoring and early warning fire prevention system for environmental smoke in a thermal power plant, and the system comprises the following parts of a control module; a gasdetection unit comprising an SO2 gas sensor, a NO gas sensor, a CO gas sensor, a CO2 gas sensor and an O2 gas sensor; a ventilation connection end comprising an air inlet pipe and a ventilation automatic control valve, wherein the air inlet pipe is threadedly installed at the air outlet of the ventilation connection end, and the ventilation automatic control valve is fixedly installed outside theair outlet away from one end of the ventilation connection end by bolts; and a fire extinguishing connection end. In the invention, the fan outside the plant generates wind, transmits the external wind into the main pipe through the air inlet pipe, and then transmits the external wind into the plant through the shunt pipes and the outlet, so that the flow of air in the plant is accelerated and thecontent of various gases in the air in the plant is reduced, thereby avoiding dangers.