Since transiting from the Roman Republic to Roman Empire, Rome experienced not only changes in the political system but also its expansion in Britain. After Caesar and Augustus, Rome had a short peace period, but then Claudius launched wars against Britain. This paper focuses on the Roman Conquest of Britain and its connection with Roman state power and aims to discuss how the journey of the conquest of Britain reflects the changing power of Rome during the times of the Julio-Claudian Dynasty. The main discussion section is divided into four subsections: the war of Actium and the postponement of military, policy not to initiate military expansion, Claudius's conquest of Britain-solving the internal crisis and external aggression, and Boudicca's revolt. It is found that when Rome was internally stable and wealthy, the conquest of Britain went well, and vice versa. There is a positive correlation between the political state of the Empire and the degree of military expansion. This paper will not only provide a new perspective for the study of the Roman Empire, but also provide a historical reference for the study of the relationship between modern state power and war.