The invention discloses a passive residual heat removal system of a marine nuclear power device. The passive residual heat removal system comprises a containment and a cooling heat exchanger. The containment is internally provided with a reactor pressure vessel, a loop cool pipe section, a loop heat pipe section, a steam generator, a refueling water tank, a 1# residual heat removal heat exchanger, a 2# residual heat removal heat exchanger and a cooling water pipe bundle; the refueling water tank is arranged at the top of the containment; the reactor pressure vessel and the steam generator are connected with the heat pipe section through the loop cool pipe section; the inlet and the outlet of the 1# residual heat removal heat exchanger are respectively connected with the loop heat pipe section and the loop cool pipe section; a main steam pipeline and a water supply pipeline which are connected with the inlet and the outlet of the 2# residual heat removal heat exchanger are arranged on the steam generator; upper and lower ends of the cooling water pipe bundle are respectively connected with the inlet and the outlet of the cooling heat exchanger. The passive residual heat removal system of the marine nuclear power device is independent from external power, is improved in capability of removing residual heat of reactor core through natural circulation, is improved in safety redundancy, power and operation stability, and guarantees operation safety of nuclear reactor.