A good understanding on the microdynamics of the water absorption of poly(2-hydroxyethyl methacrylate) (PHEMA)-based contact lens is significant for scientific investigation and commercial applications. In this study, the time-dependent ATR-FTIR spectroscopy combining with the perturbation correlation moving-window two-dimensional (PCMW2D) technique and 2D correlation analysis was used to study the topic of the microdynamics mechanism. PCMW2D revealed that D2O spent 3.4 min to penetrate into the contact lens. PCMW2D also found the PHEMA-based contact lens underwent two processes (I and II) during D2O absorption, and time regions of process I and II are 3.4-12.4 min and 12.4-57.0 min. According to 2D correlation analysis, it was approved that process I has 5 steps, and process II has 3 steps. For process I, the first step is D2O hydrogen-bonding with “free” C=O in the side chains. The second step is the hydrogen bonds generation of O?H···O?D structure between D2O and “free” O?H groups in the side chain ends. The third step is the hydrogen bonds generation of D2O and the “free” C=O groups close to the crosslinking points in the contact lens. The fourth and the fifth steps are the hydration of ?CH3 and ?CH2? groups by D2O, respectively. For process II, the first step is the same as that of process I. The second step is the hydrogen bonds breaking of bonded O?H groups and the deuterium exchange between D2O and O?H groups in the side chain ends. The third step is also related to the deuterium exchange, which is the hydrogen bonds regeneration between the dissociated C=O groups and the new O?D.