Direct-current arc plasma has the characteristics of high core temperature and clean environment, and the prepared powders have high sphericity and spheroidization rate, making it an important technology for the large-scale production of high-quality powders for additive manufacturing. In this paper, spherical tungsten powder was prepared by direct-current arc plasma spheroidization technology using irregular tungsten powder as raw material. The effects of different feeding rates and powder delivery gas flow rate on the properties of spheroidized powder particles were studied. Three transformation mechanisms in the process of spheroidizing irregular tungsten powder were proved. Under a large powder delivery gas flow rate, spherical tungsten powder with nanoparticles was synthesized in-situ by direct-current plasma spheroidization technology. The morphology, phase, particle size distribution, flowability and apparent density of spheroidized tungsten powder particles were analyzed and characterized by scanning electron microscope, X-ray diffraction, laser particle size analyzer and powder flowability tester. The results show that the phase of tungsten powder particles does not change after direct-current plasma spheroidization, presenting a single tungsten phase. The tungsten powder particles prepared at a feeding rate of 8 r·min-1 have a smooth surface and a spheroidization rate of more than 98%, and the particle size distribution is narrower than that of raw tungsten powder. The flowability of spheroidized tungsten powder reaches 5.35 s·50 g-1, which is 13.18 s less than that of raw tungsten powder. The apparent density is increased from 5.37 to 11.67 g·cm-3, which is increased by 117.3%.