In fiber-optic communications, in order to achieve more data channels in the wavelength division multiplexing (WDM) system without changing the modulation wavelength range, a new type of small-sized narrowband polarizing beam splitter was designed. It can be used for data communication network expansion and improve the Signal to Noise Ratio (SNR) of the optical signal. Two kinds new film system designed were deposited on the polarizing beam splitter. One layer is narrowband filter film, while the other layer is polarizing beam splitter film. TFCalc software was used for simulation analysis, and the results shown that the bandwidth of the narrowband filter film was about 0.4 nm, and the permeability of p light from the polarizing beam splitter film was better than 99.8% in the range of 1 530～1 560 nm. Based on the above film system design, two groups film system was made on BK7 optical glass. In the experiment, light through film was spectral analysis with Agilent 8164-A type optical measuring instrument. Experimental results show that the actual bandwidth of the narrowband filter film is better than 0.4 nm, gain flatness is not less than -0.05 dB. It has a narrower bandwidth compared to the existing common 0.8 nm filter film, and it can be realized to increase the amount of data channels in the wavelength division multiplexing system with the same modulation wavelength range. Actual transmittance of p light was 99.6% through polarizing filter film, and it’s slightly lower than the simulated values, but it remains better than the design requirements. Compared to conventional polarizing beam splitter, its optical signal was stronger, and it has a higher SNR. In summary, the polarizing beam splitter has better application value and practical significance.