George Bernard Shaw’s play Pygmalion and the musical-film adaptation My Fair Lady share a highly similar narrative framework, yet differ profoundly in narrative logic, aesthetic effects, and thematic implications. Drawing upon adaptation theory and the perspective of intertextuality, this paper conducts a comparative analysis from three dimensions: narrative medium, audio-visual rhetoric and characterization, revealing the fundamental shifts of the two art forms between intellectual debate and sensory immersion, as well as social critique and romantic myth. The analysis shows that the film’s apparent fidelity to Shaw’s text is merely superficial; its genre conventions, especially the Hollywood musical’s preference for closure and emotional gratification, systematically dilute Shaw’s satire on class hypocrisy and patriarchal oppression, while softening Eliza’s final rejection of Higgins into an ambiguous, potentially reconciliatory finale. The study thus contends that adaptation is never a neutral transfer but a culturally embedded reinterpretation, and this finding provides a critical reference for evaluating screen adaptations of classic literature, particularly in terms of how medium-specific constraints and ideological contexts reshape narrative meaning.