Abstract: Sub-micrometer sized scandia, barium, calcium and aluminum co-doped tungsten powders had been prepared by spray drying method combined with two-step hydrogen reduction.The powders morphology, elements distribution, particle size distribution and phase transformation process of reduction were characterized by scanning electron microscope (SEM), laser diffraction particle size analyzer, energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively.The experimental results show that the morphology of the processor powders prepared by spray drying have spherical shape, and the obtained co-doped tungsten powders have the average size of around 400 nm and elements distribute evenly in the powders.The reduction mechanism of decrease in the co-doped tungsten powders particle size has been discussed by temperature program reduction (TPR) in this paper.