Abstract: For the preparation of ThO₂ pellet meeting to heavy water reactor (HWR) fuel element technical requirements, ThO₂ powder made by oxalic acid precipitation process was used as raw material. The ThO₂ pellet was prepared through the granulating, pressing and sintering process. The effects of granulating, pressing and sintering process on the grain size and density were analyzed. The results indicate that the specific surface area of powder, press force and sintering temperature are the main effect factors of pellet density. The driving forces of ThO₂ pellet sintering and grain growth increase with specific surface area of ThO₂ powder, and the ThO₂ pellet with larger grain size can be acquired by using the higher specific surface area of ThO₂ powder. The ThO₂ pellet which can meet the HWR fuel element technical requirements of density and grain size can be prepared under the vacuum or argon atmosphere and high sintering temperature.