In this study, the compressive, split tensile, and flexural strengths of concrete with nano-CaCO3 only were compared with those of concrete with nano-CaCO3 and basalt fibers through field experiments, and the underlying mechanisms were analyzed by the Scanning Electron Microscope (SEM) techniques. On the mesoscale, a damage model of concrete was established based on the continuum progressive damage theory, which was used to investigate the influence of different lengths and contents of fibers on the mechanical properties of concrete. Then, the experimental and numerical simulation results were compared and analyzed to verify the feasibility of model. The results show that nano-CaCO3 can enhance the compressive strength of the concrete, with an optimal content of 2.0%. Adding basalt fibers into the nano-CaCO3 reinforced concrete may further enhance the compressive, split tensile, and flexural strengths of the concrete; however, the higher content of basalt fiber can not lead to higher performance of concrete. The optimal length and content of fiber are 6 mm and 0.20%, respectively. The SEM result shows that the aggregation of basalt fibers is detrimental to the mechanical properties of concrete. The numerical simulation results are in good agreement with the experimental results. © 2022, Wuhan University of Technology and Springer-Verlag GmbH Germany, Part of Springer Nature.