Diffusion bonding of micrometers thick U-Al sheets by hot pressing in vacuum was carried out under different temperatures, pressures and holding times. We have carried on the microscopic analysis, energy spectrum analysis and nanoindentation test to the bonding interface. The appropriate process parameters without diffusion layer were 350 ℃/ 63 MPa/ 1 h. Under the precondition of 1 h holding time, the process parameters for homogeneous diffusion layer were 400 ℃/ 80 MPa. The composition of homogeneous diffusion layer was mainly UAl2.