Using a hybrid simulation method that combines a lattice Boltzmann approach for the flow and a molecular dynamics model for the polymer, we investigated the polymer escape from a confining nanotube in a reverse flow. We demonstrate the substantial disparity in escape dynamics of the confined polymer for the cases with and without the reverse flow. Our simulations confirm the existence of a reverse critical velocity flux, which results from a balance between the entropic force (confinement free energy) and the hydrodynamic force (velocity of the flow). Furthermore, we find that the increase in the velocity flux reduces the escape velocity of the polymer, whereas the influence of variations in the diameter of the confining nanotube on the escape velocity of the polymer remains insignificant. The increasing velocity flux forces the polymer to escape along the boundary of the nanotubes with a stretched conformation. This phenomena turns less obvious with the increase in the diameter of the confining nanotube. Our work confers new insights into understanding the microscopic dynamics of the polymer escape from a confining nanotube in a reverse flow and provides guidance for the design of functionalized nanometer-scale fluidic devices.