Abstract: A core-shell composite zeolite (HY/silicalite-1) was prepared by modifying HY zeolite with silicalite-1 and characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), N₂ sorption and IR spectra of pyridine adsorption (Py-FTIR); the catalytic performance of HY/silicalite-1 composite zeolite in the hydrolysis of cellulose was then investigated in comparison with that of HY. The results show that the crystallization time has a significant influence on the crystal growth of the HY/silicalite-1 composite zeolite and the relative content of two components. With the optimum crystallization time of 16-24 h, a core-shell structure for the HY/silicalite-1 composite zeolite is achieved, where the silicalite-1 crystal grows over the surface of HY zeolite; with the prolongation of the crystallization time, the morphology of the composite zeolite changes from rough turbid to smooth and eventually to scale-like surface. The amount of Br nsted acid sites decreases first and then increases with the increase of the crystallization time, whereas the amount of Lewis acid sites changes in the opposite direction. In particular, the HY/silicalite-1 composite zeolite obtained with a crystallization time of 24 h exhibits excellent catalytic performance in the hydrolysis of cellulose to glucose; over it, the yield of glucose reaches 45.8% at 130℃, much higher than the value of 28.0% over the HY zeolite.