Abstract: The "sky window" policy, as a crucial reform measure for the construction of the national park system, plays a key role in coordinating ecological protection and sustainable community development. To scientifically evaluate the impact of this policy on the livelihood capital of farmers within national parks, this research adopted a quasi-natural experiment design using Wuyi Mountain National Park as a case study. Based on the farmer survey data before and after the implementation of the policy, a difference-in-differences (DID) model was employed to explore the heterogeneous characteristics of farmer types and regional distribution. The findings reveal: (1) The livelihood capital of farmers in gap communities decreased by 2.6% compared to rural communities; (2) The implementation of the policy had a significant negative impact of 4.0% and 2.9% on purely agricultural and mixed agricultural farmers, respectively; (3) Regional heterogeneity analysis shows that the livelihood capital of gap communities in Fujian and Jiangxi regions decreased by 3.1% and 3.5%, respectively. Based on the empirical results, the following measures are recommended to promote the sustainable development of rural communities in national parks: improve the differentiated governance system of the park; establish a precise ecological compensation mechanism; optimize the support model for farmers′ livelihood transformation; and formulate regional coordination policies with a focus on spatial justice.