To foster high-quality tourism development, minimize investment errors, and revitalize dormant projects, understanding tourism demand is essential. The core of this demand lies in the fluctuating internal travel needs of tourists. However, current research predominantly examines the categories of travel needs and the impact of tourists' life cycles, neglecting the patterns of travel needs change across various stages of the travel career. Consequently, the fundamental principles governing these changes remain obscure. The study identifies three trends in the evolution of tourists’ travel needs throughout their careers: the breadth of tourism, which reflects an increasing desire for novelty; the height of tourism, indicating a rising pursuit of quality; and the depth of tourism, showcasing a growing demand for deeper thought, more intense emotions, greater relaxation, and more challenging experiences. These trends are the result of the law of diminishing marginal utility, hedonic adaptation, and the addiction mechanism based on flow theory. This research provides a new theoretical perspective and a new research approach for the research on tourists’ internal needs.