Roles in a movie form a small society and their interrelationship provides clues for movie understanding. Based on this observation, we present a new viewpoint to perform semantic movie analysis. Through checking the co-occurrence of roles in different scenes, we construct a roles' social network to describe their relationships. We introduce the concept of social network analysis to elaborately identify leading roles and the hidden communities. With the results of community identification, we perform storyline detection that facilitates more flexible movie browsing and higher-level movie analysis. The experimental results show that the proposed community identification method is accurate and is robust to errors.