Abstract: To discover the pulverized coal drifting law in the high temperature and high pressure (HTHP) separator of coal liquefaction unit,the physical model was established on the basis of separator’s structure and physical character- istics of multiphase flow,the volume of fluid ( VOF) model and the discrete phase model ( DPM) were used in this numerical simulation to analyze the influence of solid phase mass concentration and particle diameter on the pulverized coal drifting characteristics in HTHP separator. The results show that the mean particle concentration is the largest at gas-liquid interface,and it increases with solid phase mass concentration. There is a negative correlation between pul- verized coal drifting ratio in gas outlet and particle size because small particles follow airflow well,and the pulverized coal drifting ratio basically remains unchanged in the same particle diameter when solid phase mass concentration in- creases to more than 7% . The pulverized coal drifting ratio can be reduced from 2. 03% to 0. 88% by using a 45° in- clined baffle in the upper part of HTHP separator.