Basalt fiber is an inorganic, eco-friendly natural fiber with high temperature resistance, corrosion resistance, a high elastic modulus, and low production costs. It enhances the mechanical properties of concrete. Through tests on cubic compressive strength, flexural strength, and axial compressive strength of basalt fiber-reinforced concrete, we investigated the effects of fiber length (12 mm and 18 mm), volume fraction (0.1%, 0.2%, 0.3%), and mixing method (single-length fibers vs. a 1:1 mix of two lengths) on concrete’s mechanical properties. We also analyzed the reinforcement mechanism of basalt fiber in concrete. The results showed that, compared to plain concrete, the incorporation of basalt fiber increased the cubic compressive strength, flexural strength, and axial compressive strength by 14.98%, 20.45%, and 15.25%, respectively. Mixing fibers of different lengths had a better improvement effect than using single-length fibers. Therefore, a well-designed mixing scheme for basalt fibers can effectively enhance concrete’s static mechanical properties. Further discussion on the reinforcement mechanism of basalt fiber-reinforced concrete provides insights for optimizing the performance of concrete and its components.