The invention discloses a passive decay heat removal system for a liquid metal cooling pool type reactor. The passive decay heat removal system is composed of a coolant inlet, a gravity-type heat pipe, an upper partition plate, a lower partition plate, a box body, a coolant outlet, a gas riser pipe, an exhaust stack, a thermal isolation layer, pipelines connected between devices, and valves. According to the invention, when a reactor is under accident states like station blackout, water supply interruption of a main heat exchanger or earthquake, a ventilation door of the exhaust stack is opened; cold air from the interior of a reactor containment enters into the box body through the coolant inlet, cools the condensing section of the gravity-type heat pipe and enters the gas riser pipe from the coolant outlet; hot air flows out of the reactor containment through the gas riser pipe; thus, the process has passive characteristic. The passive decay heat removal system provided by the invention has simple structure, is convenient to start, can simultaneously remove core decay heat and prevent radioactive substances in a reactor pit from escaping, and has passiveness, independence and high reliability.