The utility model relates to a device and a method for reducing and diluting copper converting slag. The device is a P-S converter provided with two tuyeres which are symmetrically arranged on two sides of a furnace body and are respectively 1.5m to 2.1m away from an end wall. The tuyere arranged at the position of an outer wall inlet downwards inclines with an angle of 10 degrees to 30 degrees, and an outlet is formed on a fireproof brick inner wall. A combustion spray gun is arranged on an opening arranged on the converter end wall, and an insulation layer is additionally arranged on fireproof materials of a converter fire hole. By means of the device, slag with low copper content is performed separation of the slag and sulfonium, and melt with high copper content returns back to the converter for converting. The copper content in the slag is transformed into copper matte in a phase mode. A melting point and viscosity are improved, thereby facilitating the settlement separation of the copper matte from the slag and improving direct yield of the copper in converting process and recovery rate of copper pyrometallurgy.