Swden, Norway, Denmark implemented Social Democracy and kept stable party system in the 30’s of the 20th century. After 1930’s, Social Democratic Party held the reins of government, maintained their predominance and expanded the unique model in the Scandinavian region.These three countries developed fast under the regime of Social Democratic Party.Each country has similar and institutionalized welfare policies; moreover,market economy, parliamentarism and welfare system are combined by powerful state apparatus.About the integration of the European Union, the three countries drafted different measures and suspected supernationalism of EU;the common ground is to preserve the independence of national sovereignty and ensure national interests. Therefore,this thesis mainly explores political, economic and social sections of the Scandinavian States, proceeds the further approach, especially on the historical elements and features.In addition,these three states fronted the contradiction between domestic and diplomatic affairs, how to Adjust? There are four key points in this thesis.They are,first,the development of the major party and Social Democracy in Scandinavia;second,Social Democratic Party and its main policy;third,the competition among the five parties in its country;and last,this part approaches the relationship between the Scandinavian States and EU. In the end,we assess the effects from the purpose,the implementation and the evaluation of the programme.