The present invention relates to a method of producing W—Cu based composite powder, which is used in heat-sink materials for high-power integrated circuits, electric contact materials, etc, and to a method of producing a W—Cu based sintered alloy by using the composite powder. The method of producing tungsten-copper based composite powder includes first preparing composite oxide powder by dissolving ammonium metatungstate, [(NH4)6(H2W12O40).4H2O], as water-soluble tungsten salt, and copper nitrate or copper acetate in water to the desirable composition, followed by spray-drying and calcining; then preparing a tungsten oxide powder by separately calcining a tungsten-containing salt, such as ammonium paratungstate, (NH4)10(H10W12O46); forming ultra-fine tungsten-copper based composite oxide powder by mixing 20˜75 wt % of the composite oxide powder and 80˜25 wt % of the tungsten oxide powder to the desirable composition, followed by ball-milling; and reducing the ultra-fine tungsten-copper based composite oxide powder at temperature of 650˜1,050° C. If the composite powder is molded into a certain size and sintered thereafter in temperature of 1,110˜1,450° C., a W—Cu based sintered alloy of superior thermal and electric conductivities can be obtained thereby.