The main ingredients and morphologies of residues from catalytic liquefaction of bagasse with acid functionalized ionic liquids in subcritical water were analyzed by using Fourier transform infrared spectroscopy(FT-IR)and scanning electron microscope(SEM).The relationship between surface morphology of liquefaction residue and acid strength of ionic liquid catalysts and process parameters，such as reaction temperature and time，were also investigated.The results showed that lignin and some refractory aromatic components were main ingredients of liquefaction residue.It also demonstrated that surface morphology of liquefaction residue was affected significantly by acid strength of catalyst and was much more temperature dependent.Both stronger acid and elevated liquefaction temperature resulted in higher degree of liquefaction and much coarser surface of residue.