Path coefficient, p test value and R2 value of policy influence ecosystem. Display omitted •Policy implementation is a key element of ecological governance.•Policy factors play a important role in the evolution of the Tianzhu ecosystem.•The adjustment of planting industry is the key to ecological improvement.•To strengthen the intensity of grazing and other animal husbandry policy research. Policy is a key element of ecological governance, however, insufficient attention has been given to how different policies and regulations in a systematic way affect ecosystem processes and functions. This study evaluated the impact of ecological policies in the national key ecological functional areas (NKEFAs) since 1990, taking Tianzhu County as a case study. We first evaluated the change in policy intensity through quantitative analysis of policy texts, then analyzed the change in the ecosystems with carbon storage, habitat quality, ecosystem service and water conservation. Finally, the partial least squares (PLS) was used to quantify the effective path for and effect of policies on the ecosystem through adjustments in agriculture, animal husbandry and population. The results showed that policies have a significant direct impact on the agricultural planting industry, animal husbandry and population size and structure, and have a significant indirect impact on the whole ecosystem. The research demonstrated the usefulness of applying PLS-SEM and ecosystem function indicators to evaluate the impact of ecological governance policies on ecosystems in NKEFAs. The research can provide reference for the ecological policy making of NKEFAs.