The invention discloses an integrated SCR metering injection system. The integrated SCR metering injection system includes a metering injection unit and a water heating unit for heating the metering injection unit. The metering injection unit includes a pump body, a membrane pump and a metering valve. The water heating unit includes a water inlet joint, a water inlet pipe, a water outlet pipe and a multi-section water circulation pipe communicated with each other. The water heating unit is used for heating the metering injection unit by heated engine cooling water, so that the heated engine cooling water passes by the metering injection unit directly to improve the recycling rate of energy.