Abstract: In order to investigate the reinforcement and toughening mechanism of basalt fiber reinforced concrete under impact load, this paper prepared BFRC specimens with different fiber lengths (6 mm, 12 mm, 18 mm) and volume contents (0.2%, 0.4%, 0.6%), and conducted dynamic impact compression tests using a Separated Hopkinson Pressure Bar (SHPB) system. The experimental results show that the dynamic compressive strength of BFRC has a significant strain rate strengthening effect, and under the same fiber content, the strengthening effect of 6mm short fiber is the best. Based on experimental data, this article recalibrated the Holmquist-Johnson-Cook(HJC) constitutive model parameters applicable to BFRC, and the numerical simulation results reproduced the dynamic mechanical response and failure mode of the specimens well. Using CT imaging technology, a three-dimensional structural map of the pore distribution in BFRC was reconstructed, and the porosity of different BFRC specimens was calculated. The results showed that the fiber content had a non monotonic effect on the internal porosity of BFRC, which was first suppressed and then promoted. Among them, 0.4% is the optimal value within the existing dosage range, at which the material porosity was the lowest and the macroscopic mechanical properties were the best. Research has shown that through macro micro multiscale analysis, the modified HJC constitutive model can effectively characterize the nonlinear dynamic mechanical behavior of BFRC, providing theoretical reference for the design and evaluation of the impact resistance mechanical properties of basalt fiber reinforced concrete.