To investigate the effect of central gas velocity and plasma power on the spheroidization of irregular copper powder, three radio frequency (RF) plasma torches were established. Relationships between the spheroidization rate and central gas velocity or plasma power were studied. The morphology, particle size distribution and phase composition of the powders before and after spheroidization were analyzed by metallographic microscope, laser particle size analyzer and X-ray diffractometer. The relationship between heat absorption of powder and plasma power is also explained by the theoretical calculation. Results show that the optimum parameters for the preparation of spherical copper powders are 1.6 m3/h central gas velocity and 8.1 kW plasma power. Under this condition, the percentage of spheroidization can reach 91%. After plasma treatment, the copper powders have regular shapes, smooth surfaces and no inner pores. Because the power of 8.1 kW is enough to melt the powders completely. Below 8.1 kW, the main factor affecting the spheroidizing rate is the plasma power. Exceed that, the stability of plasma jet is the main factor.