Abstract: This paper reports a study on basalt fiber reinforced concrete (BFRC) combining field test, scanning electron microscope (SEM), and numerical simulation, focusing on the mechanism of basalt fiber influencing concrete compressive strength. The influence of fiber content and fiber length is experimentally observed by conducting compressive tests on samples at different ages, and its SEM data are used to analyze the microstructure. We develop a mechanics model of concrete damage at the microscopic level based on the Mori-Tanaka algorithm and the progressive damage theory of continuous medium, and use it to examine the coupling effect of different fiber contents and different fiber lengths on the compressive strength. To verify its feasibility, the simulation results are compared with our experimental measurements and both agree well. The results show that adding basalt fiber to concrete improves compressive strength and the fiber length of 6mm is better. SEM images show that the phenomenon of fiber adhering and the weak layer between the fiber and the interface have an adverse effect on compressive strength, but the resistance of fiber against cracking leads to a considerable increase in compressive strength.