In order to study the effect of basalt fiber on the chloride ion penetration resistance of recycled concrete, the electric flux test of recycled concrete with five coarse aggregate mass replacement rates (20%, 40%, 50%, 60%, 80%) under the volume content of four kinds of basalt fibers (0%, 0.2%, 0.4%, 0.6%), and ordinary concrete were carried out. The microscopic mechanism of the effect of basalt fiber on the chloride ion penetration resistance of recycled concrete was studied from the perspective of cement hydration and pore structure by fourier transform infrared spectroscopy (FTIR) and mercury injection method (MIP). The results show that the addition of basalt fiber greatly increases the chloride ion penetration resistance recycled concrete. The combination of basalt fiber content of 0.2% and coarse aggregate replacement rate of 50% achieve the best chloride ion penetration resistance, even better than ordinary concrete. Based on FTIR, it is found that basalt fiber improves its chloride ion penetration resistance by changing the polymerization degree of hydration product C-S-H and the formation of CaCO3 of recycled concrete. Based on MIP, it is found that under the best combined dosage, the pore size distribution of recycled concrete is optimized, the porosity is the smallest, and its chloride ion penetration resistance is improved.