International clean technology diffusion is essential to mitigate and adapt to climate change, while fast and optimal diffusion can be prevented by the paywall of patents. This article explores the deficiency in clean technology diffusion caused by the legal fragmentation and rule complex of international environmental law and intellectual property law. It systematically examines three pathways to foster international clean technology diffusion through: restriction of intellectual property, including imposing external restraints in environmental law; striking internal balancing in maximizing TRIPS flexibilities; and keeping the status quo. It argues that treaty pathways may not work, and an operable pathway to promote clean technology diffusion is to maximize and consolidate TRIPS flexibilities in national laws. This option challenges the popular proposal of a “Doha-like” declaration on TRIPS and climate change due to the paralyzed multilateral trade mechanism, asymmetrical negotiation power of developing countries, prolonged negotiation process, and categorization problem in treaty negotiations.