Abstract: After the Second World War, a large number of immigrants from the colonies and the Commonwealth immigrated to Britain, which brought many problems to Britain's politics, society and culture, and Britain has also been transformed into a society with more cultural and ethnic diversity. Although the British government expressed concern about immigrants' integration as early as their arrival, the formulation of British immigration policy after the war was seriously restricted by its foreign policy. The transition from empire to the Commonwealth and then from the Commonwealth to Europe was an important factor affecting the adjustment of post-war British immigration policy. With the promotion of decolonization and the reduction of the role of the Commonwealth, the British government introduced the first legislation restricting the immigration of the Commonwealth in 1962——The Commonwealth Immigration Act of 1962, which realized the policy change from "free immigration to restrictive immigration". Since then, Britain's immigration policy has become tighter.