The high performance measuring methods to measure the optical parameters of infrared band-pass filter with complex multilayer were significantly important to improve the design and technology of the infrared filter development. Firstly, the traditional spectral measurement methods were fully analyzed, and an envelope-full spectral fitting inversion method was proposed. The basic idea, physical model and optimization algorithm of the new method were discussed in detail. Secondly, a technique for fabricating a single-layer film and infrared filter with high transmittance and wide cut-off medium-band bandpass in the 2 000-8 000 nm spectral range was designed, and the experiments to compare the difference between the actual spectrum and the spectrum calculated with the optical parameters measured by the new method were performed. The results show that the new method not only has very high precision performance, but also can identify the quality of the film process and can determine the dispersion of the film by the measurement results. The another set of experiments on the measurement of optical parameters of infrared filter illustrates that, compared with traditional full spectrum fitting inversion method, the new method not only has high-precision measurement results, but also can quickly and accurately locate the divergence between the actual plating thickness and the design thickness with the measured optical parameters, then a better high-performance infrared filter was developed.