Abstract: Agricultural heritage systems are strongly supported by traditional knowledge, which is the experience and wisdom that local residents have accumulated during their long-term adaptation to the natural environment. By acting as structural existence in agricultural heritage systems, traditional knowledge has existed in every aspect of the lives of local residents. Thus, it plays an important and necessary role in the conservation of agricultural heritage systems. In this study, we intended to define the concept of traditional knowledge from international laws and theories. According to specific characteristics of agricultural heritage, traditional knowledge is a pact of knowledge, innovation and practice that had been accumulated in long-term agricultural production and daily lives of residents in agricultural heritage systems. It is closely related to livelihood maintenance, resource management, biodiversity conservation, spiritual belief and many other aspects. It contains traditional knowledge of livelihood maintenance, biodiversity conservation, traditional skills, folklore as well as natural resource management. Furthermore, we defined each category of traditional knowledge separately, with examples, especially the Pu'er Traditional Tea Agrosystem. We analyzed the relationship between traditional knowledge and agricultural heritage system. There were 269 pieces of traditional knowledge in the system and the unique combinations of these pieces with natural, social and cultural conditions constituted a profound connotation of Pu'er Traditional Tea Agrosystem, making it a Globally Important Agricultural Heritage System (GIAHS) site. Besides, traditional knowledge had a positive impact on agricultural heritage systems in many aspects, including maintainability, enrichment of cultural values and protection of ecological environment. We also analyzed the existing problems with the protection of traditional knowledge. In Pu'er Traditional Tea Agrosystem, the physical carrier of traditional knowledge had been damaged and the transmission of traditional knowledge was now in a great crisis. Meanwhile, tourism and foreign cultures had a negative impact on traditional knowledge in agricultural heritage systems. The protection of it lacked effective measures. To conserve traditional knowledge in agricultural heritage systems, local residents were required to enhance awareness on the protection of traditional knowledge. Local government needed to integrate the protection of traditional knowledge into agricultural heritage systems conservation. There was also the need for increased investigation, collation and classification researches on traditional knowledge in agricultural heritage systems for effective protection that was in accordance with actual on-ground conditions. Inheritance of traditional knowledge needed strengthening so that the process of gradual loss of the knowledge systems could be slowed down. Existing institutions needed to be mobilized to protect traditional knowledge in agricultural heritage systems. Through these conservation actions, we could protect traditional knowledge and agricultural heritage systems while at the same time develop our own agricultural heritage systems for generations yet to come.