<p>The digital economy has become a pivotal force driving green and sustainable economic development, while the tourism industry, as a double-edged sword for ecological protection, plays an equally indispensable role. Therefore, integrating the digital economy, tourism economy, and ecological environment (DTE) into a synergistic and open system is crucial for promoting green sustainable development in the South China coastal region. This study establishes a comprehensive evaluation index system for the DTE across Hainan, Guangdong, and Guangxi (HGG) using the entropy weight method. Additionally, an obstacle degree model analyzes the key factors affecting the development of different systems. Finally, a coupling coordination model evaluates the status of green sustainable development in these provinces, quantifying the degree of synergy through coupling coordination degree (CCD). The findings reveal the following: (1) Digital economy not only effectively fosters the development of the tourism economy but also contributes to improvement of the ecological environment. (2) The levels of development in the DTE in the HGG region generally show an upward trend. (3) In terms of coordinated development of the three-dimensional system, Hainan is currently in a state of disharmony, while Guangxi has transitioned from dissonance to coordination, and Guangdong maintains a high level of coordination. (4) The key factors hindering the coordinated development of the three-dimensional system display significant regional differences. Based on these findings, this paper recommends that policymakers seize the opportunities presented by digital economy development, strengthen ecological protection, tailor development strategies to specific regional conditions, and promote system collaborative development to ultimately achieve green and sustainable growth.</p>