Mid-wave infrared focal plane detectors have been widely concerned because of their importance in military fields such as infrared guided missiles and infrared night vision devices, where the bandpass filter film has the function of filtering stray light and protecting detectors. The purpose of this study is to prepare high-performance bandpass filter film for mid-wave infrared focal plane detectors through analysis, material selection and optimization, aiming at the key technical problems of mid-infrared focal plane detector filter film. With Ge as the high refractive index material and substrate and SiO as the low refractive index material, the band-pass film system structure is designed, which not only realizes the high transmittance of 295－505 m band greater than 92% and the passband width is better than 37－48 m at 0° incidence angle. Moreover, it can achieve good cutoff effect for other bands except 295－505 m. The test results show that it has good properties such as smoothness, solidity and so on. Therefore, the filter film can be well applied to mid-wave infrared focal plane detectors.