The design theory, design steps and related important formula of the cut-off filter membrane of interference filter are illustrated in detail, and from the practical application, the 4.0~4.8 pm infrared penetration cut-off filter design process is expounded. Through the modern membrane design software optimization, the membrane layer performance is improved, and the filter to meet the requirements of the design index is prepared. The mean transmissivity of the infrared cut-off filter is less than 3.5% at 1.6~3.5 pm cut-off band, is more than 90% at 4.0~4.8 um cut-off band, and the filter layer can withstand temperature shocks from -190 C to 60 ℃, showing the accuracy of the design and the feasibility of the preparation process.