The invention discloses a cooling system for a containment of a nuclear power plant. A nuclear reactor core is arranged in the containment. The cooling system comprises a sealing shell, a water spraying device, a conversion system and a water pumping device. The sealing shell is arranged around the containment, and a closed cooling space is formed between the sealing shell and the containment. The water spraying device is mounted on the upper portion of the sealing shell, and is arranged to spray water to the upper portion of the containment. The water absorbs heat of the containment to be converted into vapor, so that the temperature in the containment is reduced. The conversion system is communicated with the cooling space so as to convert heat energy of the vapor into kinetic energy or electric energy. The water pumping device supplies the water of an external water source to the water spraying device via the kinetic energy. The cooling system can drive a vapor power conversion device by taking high-temperature water vapor as a power source, external cooling water can be supplemented constantly, cooling effect is enhanced, and safety of the nuclear power plant and even surroundings is guaranteed.