Early age hydration behavior of Portland cement containing liquid alkali free accelerators was studied by early age hydrated strength development, released ionic concentration, isothermal calorimetry, hydration phase analysis and microstructure analysis. The results show that the initial hydration heat rate of Portland cement containing liquid alkali free accelerators rises sharply due to the fast crystallization of massive ettringite prisms. The fluoride present in alkali free accelerators promotes C3S dissolution and C S H gel generation, leading to better quick setting effect and improved compatibility with superplasticizers. However, the hardening strength of cement paste hydrated 24h is declined notably with fluorine containing alkali free accelerator, mainly due to the crystallization of plate like CaF2, which absorbs and intercalates into the C S H gel structure and induces delayed hydration process.