The "two-step" sintering process of tungsten was studied, and the results showed that: "two-step" sintering can effectively reduce the sintering temperature, improve the densification of the sintered body, and coordinately control the grain size. Using "two-step" sintering, pure tungsten with a density of 99% and a grain size of 700 nm is obtained. This is one of the best sintering practices for pure tungsten reported in the literature. Compared with conventional sintering, the "two-step" sintered tungsten has a finer and more uniform grain structure, so that the "two-step" sintered sample exhibits better mechanical properties in bending and hardness experiments. Annealing experiments show that the grain growth in the completely dense sintered sample exhibits a typical parabolic growth kinetics. At the same time, the transition of grain boundary mobility is observed at 1400 ℃, and the activation enthalpy is calculated above this transition temperature. It is 6.1 eV; below this transition temperature, the grain boundary motion freezes rapidly, and the activation enthalpy increases to about 12.9 eV. This non-linear change of activation parameters with temperature indicates that in addition to grain boundary movement, defect movement such as activation entropy and corresponding triple junction lines may play a role in grain control.