Mid-infrared reflectance has significant application value for vegetation. However, due to the coupling of the emitted energy from land objects and the reflected energy from the sun in the mid-infrared band, it is challenging to determine the reflectance of land objects in this band. This article presents a model for calculating mid-infrared reflectance in vegetation, and the sensitivity analysis demonstrates that the model exhibits strong reliability. This study employed this model to calculate the mid-infrared reflectance of vegetation at multiple research sites. The values obtained were consistent with reality and showed a certain negative correlation with NDVI. A new vegetation index was established using the near-infrared reflectance and mid-infrared reflectance obtained from this model, rather than the infrared reflectance. The results showed that this new vegetation index can represent vegetation coverage and has the advantage of being insensitive to aerosols.