Tungsten is a representative refractory metal and it is hard to be fully sintered owing to its high thermal stability. In-situ tungsten nano-particle attached spherical micro-powder was synthesized in order to enhance sintering ability of tungsten powder in this study. In the RF thermal plasma, reaction pathway of injected feedstock is quite different according to the thermo-physical properties of feedstock powder. In the case of irregular tungsten micro-particle, a melting and solidification pathway is prevailing. However, tungsten trioxide micro-powder follows a vaporization and condensation pathway. In addition to the physical phase evolution, WO3 is effectively reduced to tungsten by introducing H2 in thermal plasma gas. As a result, spheroidized W micro-powder is obtained from irregular tungsten micro-powder while tungsten nano-particle is synthesized from WO3 feedstock micro-powder. Collisions between in-flight particles result in the direct deposition of nano-particles on spherical micro-particles. It is proven that nano-particles on the surface of micro-particle act as a homogeneous sintering activator because of the size effect of nano-particle during heating.