Enhancing the sustainability of the non-timber forest products industry has dual significance for both the management of local forest resources and socio-economic development. This paper adopts a systems theory perspective to construct an analytical model for the sustainable development of non-timber forest products, based on a “social-economic-natural” framework. By analyzing case studies of non-timber forest products industry sustainability from four underdeveloped counties in China, the paper derives the following main conclusions and insights: The sustainability of non-timber forest products development models is influenced by factors such as resource endowments and institutional environments and includes both single and composite models. Underdeveloped regions can achieve considerable sustainability in the development of non-timber forest products, but this requires a rational allocation of six key elements—policy, model, stakeholders, natural resources, funding, and technology—to stimulate industry growth. To promote the sustainable development of this industry, optimization should be pursued across five aspects: “policy leadership and top-level design to guide industry development”, “selection of appropriate development models based on local natural endowments and socio-economic foundations”, “large enterprise-driven mechanisms to form multi-stakeholder interest connections”, “focus on product technology research and development, and establishment of technical training mechanisms”, and “market-driven funding to develop product sales markets”.