Bacillus subtilis, Aspergillus niger spore and Aspergillus niger mycelium are chosen for samples preparation. The above three samples' reflection spectra in 2.5—15 μm band are recorded by using infrared microscopic spectrometer. From Kramers-Kronig (K-K) relationship, microbe samples' complex refractive indexes in 6—14 μm band are calculated. According to the microbe samples' absorption spectra, their water contents are calculated using the absorption characteristics of water, protein and nucleic acid. Based on the above three microbe samples' water contents and complex refractive indexes in far infrared band, biologic particle's complex refractive index model in 6—14 μm band are constructed and the model's reliability is analyzed. The construction of biologic particle's complex refractive index model has important significance in the development of rapid analysis and identification method of biologic samples, and the detection and identification technologies of biologic aerosol.