We focus on a more difficult kind of beam splitter in a cemented cube. The specification is that when the incident angle is 45°, the reflectivity in the visible range is 70%±2%, and the reflectivity at 1570 nm is not less than 90%. The film is thick, so cracking and peeling often occur after coating without ion assisted deposition on a vacuum-coating plant made in China. Some experiments are conducted after changing the beam splitter’s design, coating material, evaporation technique, and so on. Final results show that the beam splitter has good properties and can pass humidity, temperature, salt spray fog, and other kinds of environmental tests.