Abstract: Various small reactors, including the integral-type marine reactor （MRX）, have been designed and developed by Japanese Atomic Energy Research Institute （JAERI）. MRX adopts the INV-CRDM, a water-filled containment and passive residual heat removal system. MR-100G and MR-1G, the power supply system for district heating and cooling, are a self-pressurized, nature circulated integral PWR. MR-100G and MR-1C are with characteristics of low radioactive discharge and modular structure, and can be built in a city, even in the basement of an office building. Submersible compact reactor （SCR） for under-sea research vessel has similar design concept with MRX but the primary circuit is of nature circulation. The basic consideration to develop the advanced marine reactor and to enlarge their applications to other fields shows the strategic foresight of Japan. To exploit the experiences and technology in the large-scale nuclear power development in other applications in China, such as a small nuclear electricity source, the experiences obtained in Japanese small reactors can be used as references.