The complex feedback between human activities and ecological environment is always in dynamic change, especially in rural system. Farmers are connected to the ecosystem to meet their livelihood needs, and the two are interdependent and affect each other. It is of great practical significance to explore the relationship between them for promoting rural revitalization strategy and ecological protection. Taking Jiaxian County, a typical ecologically fragile area on the Loess Plateau as an example, this paper attempts to explore the dynamic relationship and mechanism between farmers' livelihood vulnerability and habitat degradation degree since the 1990s. The main conclusions are as follows: (1) From 1990 to 2020, the farmers' livelihood mode of Jiaxian County roughly experienced three development stages: traditional agricultural type, new agricultural type and non-agricultural type, the livelihood vulnerability and habitat degradation degree showed a continuous decrease, which was closely related to the transformation of farmers' livelihood types. This indicates that the impacts of different livelihoods on ecosystems are significantly different, mainly in terms of land use, resource consumption patterns, vegetation cover and biodiversity; (2) In terms of the coupled coordination types, the proportion of declining-disordered and endangered-disordered villages both continued to decrease, from 14.8% and 52.5% to 8% and 23%, and the basic-coordinated and highly-coordinated types both increased volatility, respectively, while the proportion of basic coordination and highly coordination villages fluctuated, from 26.2% and 6.6% to 49.2% and 19.7%, respectively. In terms of coupling difference types, the proportion of livelihood vulnerability prominent type and co-damage type both declined from 31.1% and 39.3% to 18% and 37.7%, and the ecological degradation prominent type and synchronization type all increased from 26.2% and 3.3% to 31.1% and 13.1%, respectively; (3) Farmers as the main actors in the rural social-ecological system, the livelihood system and the ecosystem are interdependent, and the mutual feedback relationship between the two is in dynamic change The ecosystem provides resources and living space for farmers, and at the same time, as the main management body in the countryside, the livelihood activities of farmers will have a positive or negative impact on the ecological environment. The impacts of different livelihood types on the ecosystem were significantly different, and guiding the non-agricultural diversification of farmers' livelihoods had a positive role in promoting ecological protection.