Abstract: The existence of “Online Water Army” makes the mode of depending on regarding customer comments as the criteria of judging sellers become less and less reliable in E-commerce. Based on this fact, from the buyer’s social network, authors set up a trust model for effective selection of sellers based on the social network and take the advantage of the node of social network on the evaluation feedback result of the seller to assist the customer to make a decision. The model, according to the theory of structural holes of social relations, evaluates the weight of every recommended route formed in the social network and finally gets a trust value which shows the seller’s reliability. In this paper, finally, authors take an example and show how to calculate the trust value.