Abstract: In order to study the control of grain size before the preparation of uranium-molybdenum alloy powder, the influence of the homogenizing annealing heat temperature and the molybdenum content in the alloy on the average grain size and the grain growth rate was studied after the homogenizing annealing heat treatment at 900, 950, and 1 000 ℃. The result shows that the grain growth rate and limit grain size increase with molybdenum content in the alloy and the homogenizing annealing heat temperature. In addition, the higher molybdenum content is beneficial to get the better gamma phase stability in order to get a better service performance in the reactor by measuring the degree of phase change after a thermal treatment process at 560 ℃ and 570 ℃.