With the development of the power industry and the increase in the capacity of newly-built units, the safe operation of the units is particularly important. The chemical monitoring instrument configured in the water vapor cycle system is responsible for directly monitoring the quality of water vapor, monitoring the dosage of chemical additives, monitoring pollutants, monitoring equipment operating conditions, and directly monitoring the corrosion rate, so as to monitor the water supply, condensate, and furnace. The quality of water prevents scaling and salt accumulation, slows down the corrosion of metal parts in the system, ensures the safe and economical operation of the system, and extends the maintenance cycle and service life of thermal equipment.