The invention discloses an SCR system of an electric engineering truck. The SCR system comprises an engine, an exhaust pipe and an SCR catalytic converter positioned on the downstream of the exhaust pipe, wherein a urea water ejector is arranged on the upstream of the exhaust pipe and at the front end of the SCR catalytic converter; the SCR system further comprises an electronic control unit (ECU), an air-entraining pipe and a air-entraining header pipe; a gas outlet is formed in the exhaust pipe and is formed in the upstream of the urea water ejector; one end of the air-entraining pipe is inserted in the gas outlet; the other end of the air-entraining pipe leads to the lower end part of an outer shell sleeve of the urea water ejector; one end of the air-entraining header pipe communicateswith the upper end part of the outer shell sleeve of the urea water ejector; the other end of the air-entraining header pipe communicates with an air pump; the air outlet of the air pump communicateswith at least one spraying pipe through an air injection header pipe; and each of the spraying pipes is arranged at the downstream of the urea water ejector and at the upstream of the SCR catalytic converter. The SCR system utilizes exhausted air to cool a urea water injection valve, is simple in structure and easy to operate, and can mix urea sprayed mist to facilitate improvement of the SCR catalytic efficiency.