The invention provides a method of preparing superfine alloy powder through composite codeposition and co-sintering. The preparing method includes the steps that metal powder, soluble metal salt, sodium dodecyl sulfate and boric acid are added into water and stirred uniformly to obtain a mixed solution, electro-deposition is carried out on the mixed solution for 0.5-5 h at the temperature of 35-70 DEG C and the pH value of 4-8 with the currents of 1-10 A/dm<2>, and then sediment is collected, washed and dried to obtain precursor powder; the precursor powder is placed into a sintering furnace which is vacuum or protected by inert gas, the temperature is raised to 500-1200 DEG C and then kept, and the precursor powder is calcined for 1-6 h to obtain the alloy powder. The method is simple in process and equipment, low in cost and suitable for producing alloy powder in any component proportion, the produced alloy powder is fine in particle size, uniform in particle size distribution and high in purity, the particle size is controllable, and the method is suitable for preparing the metal alloy powder of which a metal ion water solution cannot stably exist easily.