The invention discloses a system for detecting the activity of an adsorbent and relates to the adsorbent. The system is provided with a stimulation fire coal flue gas phase mercury generation unit, a reaction unit, and a detection unit, wherein the stimulation fire coal flue gas phase mercury generation unit is provided with a N2 gas cylinder, a CO2 gas cylinder, a SO2 gas cylinder, an O2 gas cylinder, a NO2 gas cylinder, a HCl gas cylinder, a NO gas cylinder, a mass flow controller, an HgO permeability tube, an Hg<2+> permeability tube, and a constant temperature water bath kettle; the reaction unit is provided with a drying oven, a mixing preheater and an adsorption reactor; and the detection unit is provided with a gas-washing bottle with solution of SnCl2 and NaOH, a gas-washing bottle with solution of KCl and NaOH, an ice-bath condenser, and a mercury vapourmeter for continuously measuring the mercury-vapor content. The system can conveniently, quickly and stably generates a fullcomposition stimulation fire coal flue gas at certain gaseous mercury concentration, and can provide stable reaction temperature and monitor the total mercury or elemental mercury content in real time by matching with the mercury vapourmeter through a rotation valve.