The invention relates to a method for preparing ultrafine tungsten-copper alloy powder, and belongs to the field of alloy materials. Ammonium tungstate and copper nitrate are burdened, ground and mixed according to the required copper content to obtain a uniformly-mixed powder raw material; the powder raw material is calcined under an air atmosphere, temperature preservation is carried out for a certain period of time, heat preservation is finished, cooling is performed, and corresponding oxide powder is obtained; then the oxide powder and carbon black less than the theoretical ratio are burdened according to a certain molar ratio, carbon thermal pre-reducing is carried out under an argon atmosphere, and powder containing a small amount of WO2 most W and Cu is obtained; and the powder obtained after carbon thermal reducing under a hydrogen atmosphere is subjected to deep deoxygenation to obtain ultrafine tungsten-copper composite powder. By using the technological process, the tungsten-copper composite powder with the crystal grain smaller than 200 nm and the uniformly-distributed size can be obtained. The method is simple in operation and low in cost and easily achieves industrialized operation. By means of the scheme, the method can also be used for preparing ultrafine molybdenum-copper composite powder.