In order to improve the spectral resolution of birefringence prism under the conditions of ensuring the quality of interference fringes image, the system used multi-level combination prisms and designed the method of interferometer fringes splice. According to calculation of the interferometer fringes intensity of multi-level combination prisms, the optical path difference function and the spectrum resolution, the present paper analyzed that the least spectrum resolution is 2.875 cm-1 in multi-level combination prisms of four prisms structure. The method of interferometer fringes splice was designed to splice the section interferometer fringes, and in experiment the size of multi-level combination prisms is 30 mm×28 mm×10 mm. The standard 635 nm laser for getting the interferometer fringes was dealed with. Experimental data show that the detection spectrum distribution of the 635.0 nm laser was distorted by the direct splicing of the interference fringes, while the detection spectrum distribution of the 635.0nm laser was consistent with the standard spectrum by the method of interferometer fringes splice. So the method can effectively avoid spectrum distortion by interferometer fringes splice in multi-level combination prisms.