The utility model relates to a nozzle of a selective catalyst reduction (SCR) injection system, and the nozzle comprises a compressed air inlet, a urea solution inlet and a measuring valve, wherein the measuring valve comprises a shell, an electromagnetic drive part and a valve body which is driven by the electromagnetic drive part, and the electromagnetic drive part is arranged inside the shell; the valve body is a hollow rod, the lower end of the valve body is provided with a ball valve, the upper end of the valve body is communicated with the urea solution inlet, and the side wall of the valve body is provided with a communication hole; the nozzle also comprises a guide sleeve, the guide sleeve is sleeved on the valve body, the upper end of the guide sleeve is connected with the shell, and a valve seat which is matched with the ball valve is arranged at the inner side on the lower part of the guide sleeve; a cavity is formed between the guide sleeve and the valve body, and the cavity is communicated with a hollow part of the valve body through the communication hole; and the compressed air inlet is arranged on the side wall of the guide sleeve. The nozzle has a good atomizing effect, and the urea solution which is remained on the wall of the nozzle can be cleaned after the injection is ended.