Abstract: The local peak heat flux behind the reattachment point is a concerned aeroheating problem in the hypersonic separation reattachment flow, especially with a large separation region. A modeling theory framework was proposed based on the characteristics of the flow and heat transfer around the reattachment zone. By applying this framework to hypersonic ramp flows with low to medium Reynolds numbers and proposing an engineering solution for the outer edge parameters of the local flow at the reattachment, the corresponding peak heat flux can be obtained. The theory was then validated by comparison with numerical simulations and experiments. Finally, the influences of size of separation region and the thickness of boundary layer on the peak heat flux were studied with the present theory.