Trust is an important causation between seller and customer in the successful network business, and the prestige of merchant is a vital factor that customers take into account when they select bargainer. In the traditional trust evaluation methods, various hypotheses are put forward for the evaluated entities, and the inveracious recommendation of malicious customers can not be avoided, so the objectivity and creditability of the evaluation result is affected. To the above questions, a mechanism scheme based on the gray system theory is put forward in this paper. It is proved that in the t time, the existence of the entity’ gray relation degree is sufficient and necessary. In this scheme, original data is firstly collected through using taste concourse method, the evaluated entities are regarded as clustering entities, and the grade point value of their key attributes given by customers are regarded as the basis of valuation. Using a gray relation analytical method, the evaluated vectors of the entities can be gotten. Through inducing and adjusting according to the arranged gray level, gray level of the clustering entity is judged, and trust degree of the entity can be obtained. The actual mark of the entity’ key attributes given by customers are regarded as the basis of valuation in this scheme. Gray number close to fact is adopted as the expressive mode so that the various hypotheses are avoided. Original data is collected through using taste concourse method and it can effectively avoid malicious recommendation. In the example, it is explained that entity’s trust is quantified and trust among entities can be compared. The scheme has some advantages, such as credible evaluation, strong maneuverability, and suiting for the automatic processing of software, etc .It is a practical and valuable new method to evaluate entity’s trust degree in network circumstance.