The invention discloses a selective catalytic reduction (SCR) metering injection pump urea crystal dissolving device which comprises a pump body and a mixing cavity installed inside the pump body, the side wall of the mixing cavity is provided with an orifice, the pump body is further provided with a flow guide pipeline, at least one chamber is formed inside the pump body, the chamber is communicated with the orifice, one end of the flow guide pipeline is communicated with fluid, and the other end of the flow guide pipeline is communicated with the chamber. The SCR metering injection pump urea crystal dissolving device is simple in structure and ingenious in design, and only purified water is required to be injected into the flow guide pipeline to dissolve reducing agent crystal inside the pump body. Meanwhile, dirt inside the SCR metering injection pump urea crystal dissolving device can be washed away, atomized reducing agents are prevented from diffusing into an air cylinder cavity to cause blocking faults of the pump body, and maintenance is convenient.