The crystallinity of lithium aluminosilicate(LAS) glass after crystallization were studied at different temperatures by X-ray diffractometry and the crystallinity of the standard glass ceramic with known crystal and glass phases was examined. The crystallization mechanism of LAS glass was analyzed by the crystallinity, with a formula relating the crystallinity (Ⅹ) and temperature (7). The results show that the calculated crystallinity of LAS glass by XRD increases with the crystallization temperature,in the range of 40% -50%, which is close to the calculated ones of standard samples with spodumene quartz ratio of 40%-70%. The activation energy of LAS glass is different within different temperature ranges; nEc is 125.44 kJ/mol at 710-810 ℃ and nEc is 17.42 kJ/mol at 810-980 ℃, which indicates different crystallization mechanisms. It has been proved that the required energy for crystallization of glass in the lower temperature range includes the interfacial energy between glass and crystalline phase and the free energy difference of atoms in structures of glass and crystal, and in the higher temperature ranges only the interfacial energy between glass and crystalline phase is considered.