High refractive index cemented beam splitting prism is widely used in aberration correction of complex optical systems, which can reduce the number of lenses and improve the image quality. However, in the process of high refractive index cemented beam splitting prism, the flatness of spectral curve is very poor, and even the spectral curve is difficult to achieve. By introducing the structure of cemented beam splitting prism, the characteristics of optical adhesive and the principle of optical wave time coherence, the prism with flat spectral curve of 420~720 nm, T:R=1:1±0.03, T+R≥95% on ZF88 high refractive index optical glass substrates is designed and fabricated. This technology breaks through the deviation effect of spectral curve for glued parts, and provides a new theoretical basis and preparation scheme for the design and fabrication of optical thin films.