The fiber-reinforced polymer (FRP) with excellent performance was prepared by modified basalt fiber (BF) to reinforce epoxy resin (EP), and the mechanical properties and thermal resistance of FRP were studied. The results show that modifying BF with the silane coupling agent KH550 increases the roughness of the BF surface. As the amount of modified BF increases, the tensile strength and flexural strength of FRP first increase and then decrease, while the impact strength first increases significantly and then increases slowly. With the increase of modified BF adding amount, the thermal stability of FRP continuously improves. When the modified BF adding amount is below 3 phr, the thermal stability of FRP is significantly enhanced. Continuing to increase the BF content, the thermal stability of FRP improves slowly. When the modified BF adding amount is 3 phr, the comprehensive mechanical properties and thermal resistance of FRP are optimal. At this point, the tensile strength, flexural strength, and impact strength are respectively increased by 56.6%, 67.9% and 86.1% compared to pure EP, the thermal resistance of FRP is enhanced, the initial degradation temperature of thermal decomposition is increased by 66 ℃, and the mass loss rate is reduced by 8.8%.