The invention provides a passive containment cooling and pressure-reducing system. A reactor is arranged in the containment. The system includes a containment pressure-inhibiting sub system and a containment cooling sub system, wherein the containment pressure-inhibiting sub system includes a pressure-inhibiting water tank and a discharge channel arranged in the containment. The containment cooling sub system can be arranged in various structures. The containment cooling sub system and the containment pressure-inhibiting sub system are passive and are free from being driven by external power supplies. In the invention, by means of the passive measurement for reducing vapor amount and reducing gas temperature, the pressure in the containment is reduced, so that not only are functions of early-stage peak clipping and pressure reducing and long-time cooling and pressure reducing satisfied but also the volume of the containment is not necessary to increase, thereby reducing design size of the containment and furthermore reducing cost.