The invention provides a melt in-pile retention passive cooling system in a nuclear reactor severe accident state, comprising a heat preservation layer runner, a heat preservation layer, a suppression pool, an upper pool, a suppression pool reactor cavity water injection pipeline, a recycling pit and a recycling pipeline, wherein the heat preservation layer runner is a fluid runner between the outer wall of a reactor pressure vessel and the heat preservation layer, a vent hole is formed in the top of the runner, and a water inlet hole is formed in the bottom of the runner; the suppression pool is arranged in a steel containment and is communicated with a reactor cavity by the suppression pool reactor cavity water injection pipeline; the recycling pit is arranged in the containment and is communicated with the reactor cavity by the recycling pipeline, the suppression pool reactor cavity water injection pipeline is provided with a control valve, and the recycling pipeline is provided with a control valve and a check valve; and the upper pool is set to surround the upper part of the steel containment. According to the technical scheme disclosed by the invention, an idea of melt retention defense in depth is adopted, so that cooling and retention of a reactor core melt as well as long-term cooling of the containment in relatively small reactor core decay heat and maximal reactor core decay are realized.