Abstract: Previous studies have discussed the trust degree calculation among network nodes and key nodes selection from the perspective of online social networks. Based on the six degrees of separation, social network and interpersonal trust theory, this paper builds two social networks of farmers by using 37 and 46 questionnaires from a typical rural village in the central and west part of China, and then proposes a method of calculating the trust degree of farmers in the social networks. The results show that the social network of agriculture marketing is simplified as a network figure with different levels. Then the key farmers in the simplified social network are identified by analyzing the degree of trust and the betweenness centrality. In addition, the case study indicates key farmers always play several roles in the village, such as the leader, retailer of agricultural materials, agricultural technicians and large farmers, who always have a good education and good relationships with others. So, an effective marketing strategy for agricultural materials is proposed based on the key farmers. This paper not only enriches the study of the trust degree and the identification of key nodes in the social network, but also inspires agricultural material retailers to formulate a reasonable marketing strategy aiming at key farmers.

Key words: social network, trust degree, betweenness centrality, key farmers