The development of sustainable tourism has various stakeholders such as local residents, businesses, governments, visitors, travel agencies, and tourism companies. Tourism destinations need to be protected not only to ensure a better travel experience but also to ensure that they can be enjoyed in the future. This study explored the degree of influence of key stakeholders such as the government, travel agencies, local residents, and tourists on the development of sustainable tourism in Haikou, the capital city of the island province Hainan, China. This city is rich in tropical natural resources and offers unique opportunities for the development of tourism. In 2018, Haikou was selected as one of the first “International Wetland Cities” by the 13th United Nations Ramsar Convention. However, the high dependence on tourism and centralized consumption have caused several ecological and environmental problems in Haikou. An online questionnaire survey of 419 stakeholders was conducted, and factor analysis was used to identify five dimensions. The structural equation modeling method was used to explore the degree of influence of different relationships on sustainable tourism development in Haikou. The results indicated that key stakeholders are most concerned about tourism awareness, ecological protection, and sociocultural development. Therefore, further efforts to promote and develop tourism must focus on ecological and environmental protection. Creating positive travel experiences and managing tourism wisely can meet the demands of today without compromising the future.