The invention discloses an overpressure protection system for a reactor cabin. The system comprises a pressure relief pipe, a multi-stage pressure relief assembly, a pressure suppression assembly anda sewage tank; the inlet end of the pressure relief pipe communicates with the interior of the reactor cabin; the multi-stage pressure relief assembly is arranged in the pressure relief pipe or on a bypass branch pipe of the pressure relief pipe; the pressure suppression assembly communicates with the pressure relief pipe; an inlet of the sewage tank communicates with the bottom of the reactor cabin through a safety drainage pipeline; an outlet of the sewage tank communicates with a radioactive wastewater treatment system; the pressure relief assembly comprises pressure relief valves and first-stage rupture discs, wherein the pressure relief valves are arranged on the bypass branch pipe, the first-stage rupture discs are arranged in the pressure relief pipe, and connection points of the bypass branch pipe and the pressure relief pipe are positioned at two ends of the first-stage rupture discs; and the pressure relief assembly further comprises second-stage rupture discs, wherein the second-stage rupture discs are arranged in the pressure relief pipe. The overpressure protection system disclosed by the invention has the beneficial effects that the multi-stage pressure relief assembly is used for carrying out grading pressure relief treatment and overpressure protection on a reactor cabin after a coolant leaks.