Quantitative analysis by Thermogravimetry (TG) is very simple for single-step transitions. However, it is impossible to perform quantitative analysis on overlapped TG transitions, by using TG alone. It is then investigated in this paper to utilize TG-FTIR to perform quantitative analysis for overlapped TG transitions. Formaldehyde solution samples were utilized as the examples. Results showed that it is possible to obtain quantitative information of the components in sample, after performing calibration experiments based on the gases evolved from sample.