Bond behavior of FRP rebars and concrete at elevated temperature are present in this paper. Commercially produced GFRP and BFRP rebars with sand coatings surface treatments were cast in concrete for the pullout tests, and the degradation of bond strength and bond-slip curve at the temperature ranging from 20-350 ℃ were obtained from the test. Experimental results indicated that the bond strength declined significantly during the glass transition temperature zones of epoxy resin, and a bond strength decay model at elevating temperature was proposed based on two controlled parameters of the glass transition temperature T_g and the decomposition temperature T_d of matrix. The model shown good agreement with our experimental results and other researcher's, and the model is also suitable for FRP bars with different fiber types and matrix materials. The bond failure of pullout specimens at high temperature is caused by the deboning of FRP core section and sand coatings. Based on the bond performance, the paper proposes a four stage bond-slip theoretical constitutive relationship model for FRP rebar with sandcoating surface and concrete at high temperature. The τ-s constitutive model at high temperature is based on the CMR and mBEP model, and the parameters in the model are proposed from the τ-s test results. The bond-slip constitutive relationship model at elevate temperature can be used for the analysis of fire performance of FRP reinforced concrete members.