Abstract: The present study investigated size distribution and degree of fragmentation / pulverization during lignite up- grading in fixed-bed reactor. The results show that with the temperature increasing from 120 ℃ to 900 ℃ ,the fraction of retention particles(25 - 13 mm) is decreased from 88. 42% to 16. 92% ,the fragmentation particles group(13-1 mm) are increased from 9. 81% to 75. 17% ,the group of particles are formed by pulverization(less than 1 mm) are increased from 1. 77% to 7. 91% (the fractions of particles at -0. 075 mm changed significantly) and 13-6 mm grain size go to the highest as 39. 58% . The degree of fragmentation and pulverization are increased with holding time and feed size as well. Gray relational analysis shows that greatest impact factor for fragmentation and pulverization is upgra- ding temperature. The effect of feed size on fragmentation is higher than that of holding time,but weaker on pulveriza- tion. The fragmentation mechanism during lignite upgrading are revealed by analysis of pore structure,apparent mor- phology and coal quality(moisture / volatile). Based on experimental behavior,the negative effect will occur during lig- nite upgrading process,as adsorbing free radicals to promote secondary reaction,enhancing ash content of tar,blocking with oil-dust mixture and dust forming.