The invention provides a monocrystalline diamond energy transmission window sheet used for a terahertz vacuum device, solving the problems in the prior art that microwave energy transmission window materials such as beryllium oxide, sapphire and electronic grade polycrystalline diamonds are high in toxicity, have high dielectric constants, are poor in solderability and the like. The monocrystalline diamond energy transmission window sheet comprises an electronic grade CVD diamond single wafer. The upper surface and the lower surface of the electronic grade CVD diamond single wafer is each provided with an annular weldable region along the rim of the wafer, part of the weldable regions are energy transmission regions, and the weldable regions are formed sequentially by metal ion implantation, annealing and metallization treatment. Ion implantation, annealing and surface metallization treatment ways are adopted to treat to-be-welded regions of the diamond energy transmission window sheetand edge metal characteristics are provided, so solderability of diamonds is improved. In this way, the prepared monocrystalline diamond energy transmission window sheet used for a terahertz vacuum device can be more easily connected with a window frame, and higher sealing tightness and sealing strength can be achieved.