As an in-situ, fast and noninvasive mid-infrared spectroscopy technology, ATR-FTIR has been increasingly applied in many engineering fields, particularly in in-situ real-time measurement of the solution concentration during a crystallization process. Water is a common solvent for crystallization, which has very strong absorption peaks in the mid-infrared range but has different spectra absorbances under different temperature. Thus, the affects from water and its temperature could not be ignored in measuring the solution concentration in the mid-infrared range. Based on the Lambert-Beer’s law, it is proposed in this paper to subtract the pure solvent spectra from the solution spectra under the same temperature to accurately measure the solution concentration. Take the L-glutamic acid (LGA) solution as a case for illustration. Three calibration models were established for comparison by using the original spectra of LGA aqueous solution, the original spectra deducted uniformly by the water spectra under room temperature (25 ℃), and the solution spectra deducted by the water spectra and measured under the same temperature, respectively. The results demonstrated that the proposed temperature-related differential spectra measurement method could effectively eliminate the influence of solvent on the spectra. The proposed method has a referential value for improving in-situ ATR-FTIR spectra measurement accuracy in practice.