In this study, the micro-dynamic mechanism of volume phase transition behavior of poly(N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) (PNIPAM-co-HEMA) hydrogel was investigated by temperature-dependent FTIR spectroscopy in combination with the perturbation correlation moving window (PCMW2D) technique and generalized two-dimensional correlation analysis. In conventional 1D FTIR spectra analysis, Boltzmann fitting curves showed that the volume phase transition temperature and the phase transition degree of PNIPAM-co-HEMA hydrogel were lower than that of pure PNIPAM hydrogel. It also showed that the PHEMA segments exhibit a similar “phase transition” behavior to the PNIPAM segments, which can be ascribed to the driving effect of the phase transition of PNIPAM segments. Furthermore, we found that the rate of water molecules being expelled out of the gel structure during phase transition changed as an anti-S shape. PCMW2D spectra revealed that the phase transition can be divided into two processes (named as I and II) upon heating, and further determined the temperature regions of process I and II to be 21.8-31.4 °C and 31.4-36.5 °C, respectively. Finally, generalized 2D correlation analysis found that both process I and II can be further divided into nine steps. From the deduced nine steps of process I, the significant role of PHEMA for the phase transition of PNIPAM segments was revealed. As for the deduced nine steps of process II, the driving effect of the phase transition of PNIPAM segments for PHEMA segments was confirmed.