Abstract: U-Mo Alloy fuel is the most promising LEU fuel that used for research and test reactors.In this paper,the diffusion and reaction behavior of U-Mo/Al-2Si is studied with the hot-pressing diffusion-couple method.The experiment is carried out in a vacuum furnace for 550～570℃ at 5～21h.The result shows that the interaction layer thickness is increasing with temperature augmenting and time prolonging.Rich in Si layer is formed in the U-Mo side with 47.4 at.% Si.From U-Mo side to Al-2Si side,U（Mo） content is decreased while Al is increased,and Si is decreased after biggest content in U-Mo side.The phase of U-Mo side is mainly（U,Mo）（Al,Si）₃,and Al side the phase is a mixture of（U,Mo）（Al,Si）₃ and UMo₂Al₂.The amount of UMo₂Al₂ is increased from U-Mo side to Al-2Si side.