A novel inversion method of optical constants of semitransparent liquid hydrocarbon fuel is developed based on inversion calculation of spectral transmittance radio of optical cell filled with glass-liquid fuel-glass configuration, and validated by measuring the optical constants of water. The measurements of transmittance spectrogram of optical cell filled with ethanol in the infrared wavelength of 2~15 μm at normal incidence are investigated by Bruke V70 FTIR spectrometer. The optical constants and thermal radiative physcial parameters of ethanol are achieved. The calculation precision of the novel method (IDTM model) is similar with MCDTM model, which is higher than SODTM and SDTM models. The transmittance capability of ethanol in the infrared wavelength of 2~15 μm is weak, and there are four absorption peaks, whose wavelengths are, respectively, 3.57 μm, 6.88~7.88 μm, 9.12~9.74 μm and 11.37 μm. The spectral selectivities of optical constants and thermal radiative physcial parameters of ethanol are stronger, whose values are urgently varied with different wavelengths.