<p>To investigate the performance of basalt fiber-reinforced concrete (BFRC) under fatigue load, a phased fatigue loading test is conducted, and the variation in the mechanical properties with the loading cycles, fiber content, and stress level is discussed. The degradation patterns of pore-structure parameters and pore-size distribution under various loading cycles are investigated, and the relationship between flexural strength and pore structure is established. The results show that the flexural strength, compressive strength, and relative dynamic elastic modulus exhibit an “ascending–descending” tendency at a stress level of 0.5, and that the inflection point of modulus reduction is earlier than that of flexural strength. The values of the mechanical properties decrease continuously at the stress level of 0.7, and the basalt fiber reduces the strength-attenuation amplitude. The average pore diameter of the BFRC reduces by 16.39–21.06% compared with that of ordinary concrete under load, and the linear rising slope of multiple injurious pores decreases, which implies that basalt fiber facilitates improvement to the pore structure during the service period. The porosity and total pore volume exhibit a high correlation coefficient with the flexural strength of BFRC under fatigue load.</p>