Mutual support for the aged is a model that organically unites multiple subjects, co construction and the process of co-construction, and sharing results with the elderly as the guidance. It is an important measure to solve the raising problem of rural old-ages, which has attracted the attention of the government. However, policy efforts have not achieved the desired effect, and farmers’ willingness to participate in mutual pension is low. Previous studies believed that mutual support for the aged originated from the relationship between human favour exchange and return. However, it ignores the essence of the transaction of endowment resources. It does not examine the internal mechanism of farmers’ participation in the mutual pension from the perspective of transaction costs. Based on Williamson’ s transaction cost theory, this paper deconstructs transaction cost into three dimensions of “asset specificity, transaction certainty and transaction frequency”. At the same time, this paper constructs an analysis framework of transaction cost, market network and farmers’ willingness to help each other for the aged and uses the data of Thousand Villages Survey to conduct empirical tests. The results show that: First, asset specificity, transaction certainty and transaction frequency have a significant positive impact on Farmers’ willingness to participate in mutual pension. Second, with the expansion of market network density and radius, the positive impact of asset specificity, transaction certainty and transaction frequency on Farmers’ willingness to participate in mutual pension is more obvious. Among them, with the increase of market network density and radius, transaction costs have a more noticeable impact on farmers’ participation in mutual pension.
