Study on vaporization process of nickel powder particles inside direct current thermal plasma can provide theoretical guidelines for improving preparation process of nickel nanopowder. In this paper, The effects of particle size, working gas flow rate and feeder rate on the nickel particle behavior in thermal plasma are investigated by coupled solution of the magnetohydrodynamic equations and particle thermodynamics equations. The research shows that small particles can be heated to complete vaporization in a shorter time owing to longer residence time in the high temperature region; Decrease of working gas flow rate and powder feeder rate can increase the energy of nickel particle get from plasma, thus Improving the quality of the final prepared nano nickel powder.