This paper conducts an in-depth exploration of the subtitle translation strategies and their effectiveness in the BBC documentary Earth's Pulse from the perspective of Relevance Theory. As a significant theoretical framework in translation studies, Relevance Theory emphasizes cognitive effort and contextual effects during the translation process, providing robust theoretical support for subtitle translation. This study selects Earth's Pulse as a case study and, through meticulous analysis of its subtitle translations, examines how the translator effectively conveys the original film’s intent while maintaining linguistic fluency and cultural appropriateness. The findings reveal that the translator employed various strategies—such as direct translation, paraphrasing, omission, and addition—to achieve optimal relevance between the source and target texts. These strategies not only ensure that the audience accurately comprehends the documentary’s content but also facilitate communication and integration between Chinese and English cultures. Furthermore, this paper discusses the significance of subtitle translation in documentary dissemination, as well as the applicability and limitations of Relevance Theory in subtitle translation research.