Abstract: At present, the research on the performance of concrete with recycled coarse aggregate and fiber is relatively sufficient, but the understanding on its performance changes after high temperature treatment is insufficient.To this end, three types of concrete, namely ultra-high performance concrete(UHPC),50% recycled coarse aggregate UHPC(50%R-UHPC),and 50% recycled coarse aggregate-1.0% steel fiber UHPC(50R-1.0%S-UHPC),were treated under high temperature(200 ℃,400 ℃,600 ℃,800 ℃).Then the mechanical properties of the concretes, including uniaxial compressive strength, elastic modulus, splitting tensile strength, and flexural strength, as well as impermeability and thermal conductivity were studied.The results indicate that the addition of recycled coarse aggregate to the concrete weakens its mechanical properties, impermeability, and thermal conductivity, resulting in a decline in compressive, tensile, and flexural strength, as well as an increase in porosity and permeability.However, the addition of steel fibers enhances the mechanical properties and thermal conductivity of the concrete, but also results in an increase in porosity and permeability.High temperature treatment weakens the concrete mechanical properties, impermeability, and thermal conductivity, and there is a threshold temperature of 400 ℃.Prior to 400 ℃,the impact of high temperature treatment on these properties is minimal, but once the threshold is exceeded, the properties weaken rapidly.With respect to both UHPC and 50%R-UHPC,the differences in mechanical properties and thermal conductivity gradually diminish with the increase of the treatment temperature.