Abstract: With hydrated lime and sodium sulphate as main materials，early strength agent was produced after ingredient mixture and homogenization.The same amounts of early strength agent were mixed with fly ash-Portland cement and Portland cement respectively，and the compressive strength and flexural strength of them at different ages were tested.The samples were also analyzed by TG/DTA and infrared spectrum.The influence of the early strength agent on the performance of fly ash cement and Portland cement was analyzed by means of macro and micro analysis.The experimental results showed that the early strength of Portland cement was significantly higher than that of fly ash-Portland cement with the same amount of early strength agent.The early strength agent had used to promote the hydration of the cement clinker in the sample，which had no obvious effect on the fly ash.

Key words: early strength agent, Portland cement, early strength