With the development of nuclear power, because of the characteristics of high safety, simplified structure and wide use, small reactors are attracting more and more attention. The development and design of small reactors to improve the safety and application of reactors is an important choice for the development of nuclear power in the future. In view of the existing small reactor technology, four kinds of reactor technologies, such as light water reactor, high temperature gas cooled reactor, liquid metal reactor and molten salt reactor, are introduced. The design characteristics and design pa...