Studying the relationships among tourism, the environment and carbon emissions is key to understanding how tourism activity affects the sustainable development of tourism in the Tibetan Plateau. Using Lhasa, Tibet, as a case study, the coupling and coordination relationships among the three systems were analysed to explore the impact of tourism behaviour on sustainable tourism development. Utilising panel data from 2010 to 2020, the carbon emissions of tourism activities were calculated using a bottom-up approach. The coupling coordination model was employed to examine the interrelationship of the economy, the ecological environment and carbon emissions. Additionally, the Tapio model was utilised to further analyse the dependency relationship between economic development and carbon emissions. This assessment of the sustainability of Lhasa’s tourism industry revealed that (1) the economy, the environment and carbon emissions are indeed closely intertwined with sustainable development and that (2) there has been a significant increase in the coupling coordination among the economy, the environment and carbon emissions from 2010 to 2020, coupled with a gradual decrease in economic dependency on carbon emissions. Despite providing favourable conditions for sustainable development, there remains considerable disparity among the three subsystems, with relatively low overall coordination. Accordingly, some practical low-carbon tourism policies are recommended to guide tourism practices and promote long-term sustainability.