The invention discloses a low-temperature preparation method of pure nano W-Cu composite powder and belongs to the technical field of refractory metal and powder metallurgy. The low-temperature preparation method comprises the steps that by taking micron-sized tungsten powder and nano-sized aluminum powder as raw materials, high-energy ball milling is carried out by mechanical alloying, and Al issubjected to solid solution into a W matrix, so that W-Al composite powder is prepared; after Al is eroded by a NaOH solution, nano porous tungsten powder is obtained; and an alcoholic solution of cupric chloride and then an alcoholic solution of oxalic acid are added separately, air gaps and surfaces are coated with a layer of cupric oxalate, through heating reduction, cupric oxalate is resolvedinto copper and carbon dioxide, carbon dioxide is eliminated with circulating argon gas, and produced copper coats the surfaces of tungsten pores. The reduction temperature is low, and growing of particles is limited to a great degree, so that the pure nano W-Cu composite powder with the particle size being below 50 nanometers is obtained.