Abstract: Four working conditions of room temperature (25℃), 200℃, 400℃ and 600℃ were designed. The failure modes and mechanical properties of steel-concrete composite beams reinforced with basalt fiber reinforced polymer (BFRP) bars after high temperature were studied by the model experiment method. The failure modes and bearing capacity of steel-concrete composite beams reinforced with BFRP bars and steel bars were studied by analyzing the test beam’s crack development, deflection deformation, temperature field and failure process. The results show that the mechanical properties of BFRP bars are significantly reduced after a high temperature of 400℃. The mechanical properties of composite beams are significantly reduced after the high temperature of 400℃ due to the deterioration of BFRP bars. The expansion of BFRP bars leads to the cracking of concrete slab, and the crack development is obviously different from that of steel-concrete composite beams reinforced with steel bars. The main cracks regularly develop along with the transverse reinforcements, and the cracks are wider. When the temperature is lower than 400℃, BFRP bars do not reach the deterioration temperature due to the wrapping of concrete, and the bearing capacity and appearance of the two steel-concrete composite beams have little difference. After 600℃, the deterioration of BFRP bars weakens the stiffness and strength of concrete slabs, resulting in a decrease in the bearing capacity of steel-concrete composite beams reinforced with BFRP bars more than steel bars. The steel-concrete composite beams reinforced with BFRP bars have larger deformation after loading due to the small overall stiffness. After high temperature, the failure modes of the two steel-concrete composite beams are similar, which are shear failure with evident elastic, elastoplastic and failure stages. At 600℃, the ductility of the two steel-concrete composite beams is significantly reduced, the plastic deformation is reduced, and the failure is more sudden. The research results can provide a reference for applying BFRP bars in steel-concrete composite beams.