This study aimed to analyze the technological innovation system (TIS) of biomass energy in Iran. The research approach was grounded in a functional analysis of the TIS framework, with data collected through expert interviews and a review of relevant documents and prior studies. The results indicate that anaerobic digestion and gasification technologies remain at the pre-development stage and face challenges such as insufficient sustainable investment, weak institutional interactions, the absence of clear regulatory guidelines, and a lack of market mechanisms. In contrast, incineration technology, supported by waste management regulations and relatively high feed-in tariffs, has entered the development stage with active private sector participation. The functional analysis reveals that, at the pre-development stage, knowledge development and diffusion, resource mobilization, and system guidance are critical, whereas at the development stage, entrepreneurship, market formation, and legitimation play more prominent roles. Nonetheless, deficiencies in knowledge diffusion, institutional fragmentation, shortages of skilled human resources, and the lack of accessible long-term low-interest financing have confined most activities to the research level. Consequently, the sustainable development of these technologies requires a comprehensive approach, including the establishment of a national steering body, reform of feed-in tariff mechanisms, implementation of pilot projects, and enhancement of research quality to facilitate the transition toward a low-carbon energy system.