Ecosystem service is the bridge linking natural ecosystem and socioeconomic system. Understanding the supply and demand of ecosystem services and their spatial matching characteristics, so as to achieve the balance of ecosystem service supply and demand, is very important to maintain regional ecological security and sustainable development. At present, the assessment methods of ecosystem service supply and demand, as well as the optimization methods of ecological security pattern, are still at the initial stage, and lack of research on future projections. In order to better understand the impact of past climate change and socio-economic development on ecosystem services and ecological security pattern, and to inform responses to different climate and socio-economic development scenarios in the future, it is necessary to systematically assess and forecast the supply and demand of ecosystem services. In this study, we quantitatively assessed and mapped the supply and demand of three ESs, namely water provision, food production and carbon sequestration, in 2000, 2010 and 2015 in Southwest China. We then projected the supply and demand of the three ESs under IPCC's (Intergovernmental Panel on Climate Change) four SSP-RCP (Shared Socio-economic Pathways-Representative Concentration Pathways) scenarios. The historical supply and demand of water provision service and carbon sequestration service showed significantly spatial mismatch, with ES demand increasing substantially from 2000 to 2015. Future projections suggest that water provisioning service is most affected by climate change, future carbon sequestration is faced with most uncertainties, and SSP5-RCP8.5 is the most extreme scenario under which the ES supply and demand show the substantial changes. Since this study is a relatively long-term systematic ES assessment in a large region, there are inevitably some limitations in the methods and data. However, the aim of this study is to assess and project ecological and socioeconomical changes at a large spatial scale during a long time scale, and these uncertainties have limited influence on the macroscopic results of ES changes and projections.The ongoing rapid economic development and population increase in Southwest China has resulted in a surge in ES demand and this trend is likely to continue in the future, while the future holds many uncertainties under climate change. The same is true for many other developing areas and countries. Balancing ES supply and demand is one of the key challenges for achieving sustainable development. Our study contributes to the methodology of the quantitative assessment and mapping of ES supply and demand, and is an advanced application of the SSP-RCP scenario framework.