The purpose of this study is to figure out how differently the technological trajectories of light water reactor could be shaped under the nuclear power plant regimes of four countries: the United States, the United Kingdom, France and Germany. The historical development of light water reactor technology shows also how the technology could be socially constructed. During the 1950s the AEC focused on the development of light water reactor of Navy with the policy of "Atom for Peace" in order to diffuse reactor technology for producing electricity. On the contrary the development of Gas-cooled reactor was pursued in the UK and France with the purpose of plutonium production for nuclear weapons. While the power efficiency and economical efficiency of reactor were hardly considered in the three countries, those factors were relatively high valued in Germany where the using of nuclear energy had to be constrained in the power plants. In the 1960s the light water reactor had been established as a dominant technology. With the growth of reactor market in the US the light water reactor was put to practical use for private power plants. EURATOM helped the light water reactor of the US to step into european countries. Germany took the lead to construct nuclear power plant with light water reactor, while it was at the End of the 1960s that France decided to develop the light water reactor after the technological nationalism decayed. Despite of these trends, the UK maintained to promote Advanced Gas-cooled reactors, which resulted from the momentum of nuclear power plant regimes. During the 1970s the nuclear power plant regimes of France and Germany were stabilized on the base of nuclear industrial growth and new energy policies. The reactor industries in France and Germany made contribution to globalization of light water reactor. There accumulated opportunities to learn technology with increasing number of light water reactor with large scale. The economic efficiency of nuclear power plant was also improved. However the UK had not introduced the light water reactor until 1979. The british power plant regime allowed engineers only to invent a "british light water reactor", which differed from american light water reactor in terms of safety. The social shaping of technology is also found in the case of light water reactor in four countries. (Dongguk University-Seoul, Dharma College/minerba64@naver. com, Sookmyung Women`s University, Dongguk University, Chonbuk National University)