Hainan Island in southern China has strong ecological systems and natural resources relevant to multiple Sustainable Development Goals (SDGs). The island has been focusing on economic development and building a national park and a free trade port to improve the economy and people’s lives. However, current research on Hainan’s SDGs has mainly focused on urban-related indicators (SDG11), resulting in an incomplete evaluation across SDGs. It is necessary to establish a comprehensive assessment framework that incorporates a greater number of indicators for Sustainable Development Goals in Hainan. Based on the United Nations Sustainable Development Assessment System and the current situation in Hainan, a localized study has been conducted on indicators for Sustainable Development Goals 1–4 and 6–11. Our analysis of target scores, SDG scores, and SDG index scores shows the following: (1) The sustainable development of Hainan Island has significantly improved since 2015, with SDGs 1, 3, and 10 showing the largest improvement; (2) most cities and counties have increased their SDG index scores, with Sanya City replacing Haikou City as the top scorer in 2021; and (3) the sustainable development levels are unevenly distributed, with high levels in the north and south, stable levels in the east, and low levels in the central and western regions. Policies, such as the “Haicheng Wending” comprehensive economic circle, are promoting integration between cities and counties. The study provides a localized evaluation framework and methodology for SDGs assessment at the regional level that can serve as a reference for similar work on sustainable development in similar regions and tropical islands worldwide.