This paper presents a comprehensive trust model mainly for the problems existed in the current assessment of trust in online auctions. The credibility of an auction participant usually can be assessed by multiply attributes of trust such as recent credibility, time weight, value of the transaction, etc. Different participants in online auction have different viewpoints on the trust. By means of evaluating the assessments of credibility with multi-viewpoints of different participants, we calculate credibility of participants separately. The comprehensive model is able to greatly improve the accuracy of calculation. Thus, it is more effective for analyzing the credibility of participants in online auction.