Abstract: Over the past century, China's hydrological and meteorological observations in the South China Sea (SCS) have evolved from being sporadic to systematic and then to a multidisciplinary comprehensive network, offering copious data for extensive and in-depth research on the variations of heat and salt in the SCS. Thus, a solid foundation has been laid for enhancing short-term climate prediction and protecting the marine ecological environment. This paper briefly reviews the research progress on multi-scale variations of heat and salt in the SCS and their climatic and ecological effects over the past century. Among them, the section on heat and salt variations in the SCS is mainly summarized based on different time scales, encompassing the characteristics and control mechanisms of seasonal to intraseasonal, interannual, interdecadal, and long-term variations, as well as marine heatwaves, salinity variations and their impact on heat balance. This paper clarifies the impact pathways of multi-scale climate modes in the Pacific and Indian Oceans on heat and salt variations in the SCS. Regarding the climatic and ecological impacts of thermohaline variations mainly involve the effects on monsoon and precipitation, as well as the extensive effects on marine ecosystems. Finally, this paper also looks forward to the urgent issues that need to be addressed and improved in the aforementioned aspects.