Plasma Rotation Electrode Process (PREP) was used to produce high-Nb TiAl powder,the effects of process parameters on the particles sizes and distribution were systematically studied. The results showed that the particle size of as-produced high-Nb TiAl powde is mainly determined by the rotating speed and diameter of electrode bars. High electrode rotating speed and large electrode diameters lead to fine powder (less than 75μm), and the particles distribution from a unimodal distribution change to a bimodal distribution. Through analyzing the forming conditions of powder particle, putting in the high-Nb TiAl materials constants and PREP parameters, and comparing the calculate values with actual particles, an empirical formula was developed to calculate mean particle diameters of high-Nb TiAl powder produced by PREP.