Objective To explore the experience of Breakthrough Cancer Pain (BTcP) and the immediate decision-making process in patients with advanced cancer, in order to provide a reference for optimizing cancer pain management. Methods A phenomenological research method was adopted.Semi-structured in-depth interviews were conducted with 15 advanced cancer patients who had experienced BTcP.Data were analyzed using Colaizzi′s 7-step analysis method. Results The experience of BTcP and the immediate decision-ma-king process in advanced cancer patients were summarized into 5 themes and 12 sub-themes:suddenness of pain and sense of survival crisis (sudden sharp increase in pain intensity, without warning; loss of bodily control, collapse of belief); immediate assessment and progressive decision-making during BTcP episodes (immediate assessment; decision nodes); diversity of coping strategies (coexisting with the pain; seeking help from others; utilizing environmental resources); real-world dilemmas in immediate decision-making (dilemma of drug dependence versus adverse effects; ambiguous medication guidance and poor drug accessibility; cognitive limitations at the peak of severe pain, and ineffective caregiver support); evolution of coping experience and support needs (growth and systematization of individual coping experience; urgent need for structured, personalized guidance). Conclusion BTcP in advanced cancer patients is sudden and severe.The immediate decision-making under BTcP is a dynamic process full of internal conflicts under time pressure, and is influenced by multiple factors such as insufficient medication guidance, poor drug accessibility, and inadequate caregiving support.It is necessary to build an active empowerment model centered on decision support, collaborative training, and system guarantees to optimize BTcP management.