In this study, attenuated total reflection spectroscopy (ATR-IR) was used to analyze the influence of NaOH on the hydrogen bonding network of H₂O and 1-ethyl-3-methylimidazolium acetate ionic liquid aqueous solution (EmimAc/H₂O). The results showed that the addition of NaOH affected the symmetry and type of hydrogen bond of water aqueous solution. The symmetric hydrogen bond bands Ⅰ (3 218 cm^-1) and Ⅱ (3 375 cm^-1) decreased with NaOH concentration. The hydrogen bonds of the water were polarized in the presence of NaOH, thus producing continuous absorption bands; moreover, the absorptions of the continuous bands were enhanced with increasing NaOH concentration. In the case of the EmimAc, water affects both the cation and anion. The OH of H₂O interacts strongly with COO^- of EmimAc and generates a wide absorption band between 3 400 and 3 200 cm^-1, while the interaction of proton on H₂O and COO^- makes the C＝O absorption band red-shift. H₂O addition could cause a blue shift or a decrease of the absorption between the band 1 600~1 200 cm^-1, which is referred that water could damage the original hydrogen bond network of EmimAc and form “anion···HOH···anion” and weaken the interaction between cation and anion of ionic liquid. When water was substituted by NaOH and mixed with EmimAc, the absorption strengthened. It is probably that destruction of the EmimAc hydrogen bond network by NaOH aqueous solution is not as significant as water. In summary, the EmimAc/NaOH system can be used to reduce the viscosity of the ionic liquid system and the application cost of EmimAc, which has a specific guiding significance for the pretreatment of lignocellulosic biomass.