Adjust apparatus and method of urea water solution supply apparatus

PURPOSE: A urea solution supply device and a control method thereof are provided to decrease nitrogen oxide by supplying a urea solution to a catalyst through a nozzle, and to minimize the volume by forming a regulator and a ventilation valve in one. CONSTITUTION: A urea solution supply device(A) comprises: a tank module(2) including a tank(3) stored with a urea solution, a regulation device(4) composed of a regulator(44) installed to the upper part of the tank to keep the pressure of a supply line regularly and a ventilation valve(42) varying a moving path of a urea solution, and an exterior pump(6) installed to the supply line connected to the regulating device to supply a urea solution to a nozzle; a nozzle(9) spraying the urea solution supplied from the tank module to a catalyst; a catalyst(10) attached with the nozzle to decrease nitrogen oxide by a catalytic reaction with the sprayed urea solution; a supply line(S) connecting the ventilation valve and the nozzle; a return line(R) drawing back the excessively supplied urea solution from the supply line into the tank through the ventilation valve; and a control unit(400) controlling the directional change of the ventilation valve, the on/off operation of the exterior pump and the operation of the nozzle.