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Mechanism and evolution of the pore-air natural convection cooling effect in fractured-rock embankments in permafrost regions are studied using a numerical representation of the non-dimensional governing equations in variable permeability porous media. The analyses show that winter-time natural convection in fractured-rock embankments begins to occur in the side slope portions and gradually develops from the left and right side slope portions to the middle portion of embankment. The more significant distortion of isotherms from their initial orientations due to heat conduction alone is that the cooling effect of winter-time natural convection on the fractured-rock embankment is stronger. The minimum critical Rayleigh numbers triggering natural convection of the pore-air in the side slope portions and the middle portion of embankment were obtained. The factors of influence on triggering winter-time convection cooling effect in fractured-rock embankments were analyzed. Finally, the assertion that the techniques of the fractured-rock revetment and berm are the effective measures to maintain the heat stability of the roadbed in permafrost regions is theoretically demonstrated.