From the mid-1970s to the present, Swedish nuclear power policy has changed through the interaction between nuclear power support coalition(NSC) and nuclear power opposition coalition(NOC). Since the phase-out of nuclear power was decided through a referendum in 1980, nuclear power policy has been triggered by a change of governing coalition, public opinion on nuclear power plants, and the international convention on climate change under the condition that electricity mix and power industry structure serve as long-term opportunity structure. The power mix, where nuclear power accounts for a relatively high share of power generation (34% in 2015) and the largest shareholder of the state-owned power company (Vattenfall AB), is a long-term opportunity structure that makes it difficult to phase out nuclear power plants. However, the biggest influence on Sweden’s nuclear power policy changes is political party politics and coalition shifts. In Swedish politics, where the formation of coalition governments became more common due to proportional representation, the Conservative coalition government has formed the NSC and promoted the controlled replacement of nuclear power plants by replacing the old reactor with a new one. On the other hand, the Red Green coalition government, led by the Social Democratic Party, has formed the NOC to promote the phase-out of nuclear power. Changes in public opinion related to nuclear power have affected the nuclear policy of political parties participating in the NSC and NOC. In addition, although the International Convention on climate change is consistent with the NOC, in terms of reducing fossil fuels and expanding renewable energy in power generation, it has also acted as an opportunity to reinforce the NSC. This is because the NSC does not oppose the expansion of renewable energy and argues that nuclear power is an economic way to reduce fossil fuel use and mitigate climate change. More than 40 years after the decision to phase out the nuclear plant, Sweden continues to produce nuclear power by allowing the replacement of reactors instead of permanently shutting down nuclear power plants after their end of service life. In order to solve the trilemma - power supply stability, sustainability, competitiveness - faced in the energy conversion process to reduce the use of fossil fuels, the government should consider the current state of power mix and plan the power mix from a technical and practical point of view, and strive to increase social acceptability.