SCR closed-loop control device and control method

The invention discloses an SCR (Selective Catalytic Reduction) closed-loop control device and a control method. The SCR closed-loop control device comprises a supply system, a reaction system, a control system and a power system. The supply system comprises a flow sensor and a control valve, the flow sensor is used for detecting the urea supply amount of the supply system, and the control valve is used for controlling the urea supply amount output by the supply system; the reaction system comprises a first sensor and a second sensor, and the first sensor is arranged at a gas inlet of the reaction system and used for detecting the NOx concentration of the gas inlet of the reaction system; the second sensor is arranged at the gas outlet of the reaction system and is used for detecting the NOx concentration of the gas outlet of the reaction system; the control system is in communication connection with the first sensor, the second sensor, the control valve and the power system. The power system transmits the rea