Abstract: We study the influence of different content of fly ash and water-cement ratio on concrete compressive strength, splitting tensile strength and flexural strength, and analyze the mechanism of these effects. The results show that using fly ash to replace partial cement and aggregate can make the compressive strength, splitting tensile strength and flexural strength reduced. When fly ash content is less than 20%, the falling range of 28 d compressive strength is smaller; when fly ash content is more than 20%, the falling range of 28 d compressive strength is bigger; splitting tensile strength and flexural strength is no more than 20%, the falling range of fly ash 28 d compressive strength is larger; when the fly ash content is more than 20%, the falling range of 28 d compressive strength is smaller. Compressive strength, splitting tensile strength and flexural strength of 28 d fly ash concrete will reduce with the increase of water-cement ratio. By the experiment of fly ash concrete mechanical properties, it is concluded that replacing cement at the same time, the maximum strength meets the demand of engineering practice of concrete, and test analysis showed that the best dosage from 10% to 20% of fly ash is the main factor that affects the strength of concrete.