Abstract: Based on the construction of Xiaolangdi Multipurpose Dam Project,this article reflects the test and study of the impact on the concrete performance by the fluctuation of the flyash quality of Xiaolangdi Project.The analysis of the results demonstrates that when the fineness changes between 15% and 25%,the loss of ignition varies between 4% and 12%,and the other indices meet the requirements for GradeⅡflyash, the mechanical performance,deformation and durability have no obvious change.The use of this achievement creates tremendous comprehensive benefits in the progress ensuring,cost saving and quality guarantee of the Project.