Safety of a nuclear power plant and its related systems are the first key issue to assure experts and the public of the safe operation of the plant. The AP1000 reactor is provided with passive safety systems which require no operator actions due to utilizing only natural forces such as gravity, natural circulation and compressed gas to achieve the safety function. In this paper, it has discussed about the third generation pressurized water reactor. The second generation reactors are running now. But the most important thing is to insure about the safety. Most of the protective components of the old reactors are worked by an external power or sources. But if there will be any failure in the operation of the components, then it might be dangerous. The AP1000 PWR is one of the modern reactors, which will work by natural force like gravity. So all the safety components are passive. AP1000 is also a reactor which takes less volume for its reactor.