The weak foundation of agriculture and the weak status of farmers in remote mountainous areas have become the key point restricting the comprehensive promotion of common prosperity. It is urgent to explore a mechanism to strengthen farmers and enrich the people that is more in line with regional reality. Based on the actual agricultural production, Wencheng County launched the "upgraded version" of the shareholding cooperative system -- the peasant household income guarantee shareholding cooperative system, which is an innovative practice of promoting common prosperity in backward mountainous areas and an innovative exploration of agricultural operation mechanism reform. Its organizational structure, governance mode and internal operating mechanism accord with the measurement standard of mechanism design theory. That is to say, the effective allocation of resources is realized by means of public possession of production materials and household contracting of production responsibilities, the lower information cost is realized by "enterprises + agricultural cooperatives (farmers) + scientific research institutions", and the goal of common prosperity is realized by means of participatory restraint and incentive compatibility. Therefore, it has become a successful case of mechanism design theory in the agricultural and rural areas to solve the problem of co-prosperity.