"Joker" is a comic film with a mentally ill person as the protagonist, mainly telling the story of Arthur Frank, mentally ill and engaged in clown acting work, because of the indifference of society, the betrayal of colleagues, the deception of his mother, the ridicule of his idol and various bad encounters, his spiritual world gradually collapsed, and eventually went to the road of crime. Supported by Freud's relevant theories, this paper interprets Arthur's character image from the perspective of psychoanalysis, explores the close relationship between Arthur's life experience and his own mental and psychological conditions, and analyzes the causes of his illness, the process of self-repression and the changes of personality structure.