Population and farmland are the key elements in agricultural production and significant components of the rural population-land relationship. Spatial-temporal coupling changes to population and farmland in mountainous Karst areas across Southwest China can reveal the transformation and evolution of this relationship. Such findings provide a scientific basis for agricultural land regulation, ecological restoration, and rural revitalization. Features of the population and farmland change trend in Yinjiang County were analyzed together with spatial-temporal coupling characteristics. The driving forces affecting population data, land data and their relationship with each other were investigated using an elastic coefficient model. The results showed that between 1958-2016, both the rural population and farmland extent in the mountainous karst areas across Yinjiang County rose then fell, while the opposite trend was seen for per capita farmland area; further, the results showed that from 1958-2016, the spatial-temporal coupling relationships between the rural population and farmland change across Yin Jiang County were first non-coordinated but became coordinated over time; finally, the results indicated that factors driving the formation and development of the spatial-temporal coupling relationship were mainly attributable to the combined effects of natural environment, socio-economic conditions, policy, and changes in urban-rural relations. Results revealed that the spatial-temporal coupling relationships between the rural population and farmland had significantly changed over the last 60 years in mountainous karst areas across Southwest China and that there has been a transition in the population-land relationship in rural areas. Furthermore, the results strongly suggest that ecological restoration, farmland planning, and land resource redistribution should be introduced so that rural revitalization and a sustainable population-land relationship can be achieved.