This paper proposes a novel functionally graded concrete (FGC) pavement structure, and conducts a theoretical study to compare the thermal postbuckling behavior of the FGC pavement with conventional functionally laminated concrete (FLC) and examine the effect of volume fraction index, layer thickness ratio, and initial imperfection. The structure consists of three homogeneous layers made from steel fiber rubber concrete (SRuC), geopolymer concrete (GPC), and plain Portland cement concrete (PPC), respectively, with a functionally graded layer between the homogeneous layers. The material properties of the graded layers follow Sigmoid law distribution. For FLC without graded layers, potential interlayer slip due to weakened interlayer bonding is considered. The governing equations for the thermal buckling problem of pavement with initial imperfection are derived based on the Timoshenko beam theory and von Kármán geometric nonlinearity, solved using the differential quadrature method combined with the iterative technique, then compared with the existing results to validate the validity and accuracy of the proposed formulation. The results indicate that the thermal stability of FLC is weaker than FGC due to the interlayer bonding state. The thermal buckling strength of the pavement can be improved by increasing the graded layers and optimizing the material distribution. Furthermore, the imperfection has a significant effect on the postbuckling equilibrium path.