Evaluating the relationship between protected areas (PAs) and poor households of the surrounding communities accurately is crucial for realizing the dual objectives of biodiversity conservation and coordinated development of local communities. However, limited literature has analyzed the mechanism of the impact of PAs on household multidimensional poverty from the perspective of social capital. This study investigated 787 households around 14 PAs in Sichuan and Shaanxi Provinces, constructed an analytical framework of Protected Areas-Social Capital-Multidimensional Poverty, and analyzed the impact of PAs on multidimensional poverty of surrounding rural households based on an intermediary effect model. The results show that: (1) Households inside the PAs are more likely to fall into multidimensional poverty than those outside the PAs; (2) The establishment of protected areas impairs social capital to some extent, further leading to multidimensional poverty of rural households; (3) The intermediary effect of social capital shows significant differences at different administrative levels (national and provincial), between different provinces, and between PAs with and without ecotourism. Specifically, in PAs at the provincial level, PAs of Shannxi Province, and PAs having ecotourism, social capital has larger intermediary effects. Therefore, PA management should extend rural household social networks, enhance their social trust, and mobilize their social participation to improve the quality of rural household social capital and further develop their livelihoods.