The invention aims to provide a device based on an injection pump and used for realizing emulsifying combustion of a supercharged diesel engine and reducing NOx emission. The device comprises a low-pressure-stage pressurizer and a high-pressure-stage pressurizer; a high-pressure-stage turbine and a low-pressure-stage turbine are mounted on an air exhaust pipeline; a high-pressure-stage air compressor and a low-pressure-stage air compressor are mounted on an air inlet pipeline; and the high-pressure-stage turbine and the high-pressure-stage air compressor can be cut in and cut out through opening and closing of bypass valves as required. The injection pump is further arranged on the air inlet pipeline and is used for producing vacuum in a closed container and pumping water vapor into the air inlet pipeline, and a branch pipeline where the injection pump is located can be cut in and cut out by the aid of a two-position three-way reversing valve as required. With the device, arrangement of an air inlet way nozzle and other related devices can be avoided, relatively small structural alterations are made, and the water addition quantity can be changed flexibly according to the working condition of the diesel engine, so that the combustion temperature of the diesel engine can be reduced, and NOx emission can be reduced.