This is a difficult kind of beam splitter in a cemented cube. The specification is: under angle of incidence (AOI)=55o, the reflectivity at 905 nm is no less than 85%, and in the visible range the average transmittance is 40+(-)2%, and T+R>=90%. Because the AOI is 55o, it needs to use a metal coating material to make sure the film be designed. The film has some problems on durability, and its optical performance is very hard to be controlled. We get some experiments after changing its design including coating material and evaporation technique. Final results show that the beam splitter has good properties, and passed temperature, and environmental durability.