In order to calculate the collusion intensity of government project tenderee and the bidder, based on the analysis of main items and key nodes in the overall bidding process, the type of collusion between the tenderee and the bidder is selected, and the calculation factors of the tenderee and the bidder's collusion intensity are screened out, including the bias of the review clause, the difference of the examination standard, the directivity of the bidding documents, the suggestion of the bid inviter's intervention, and the tendentiousness of the expert evaluation. The evidence reasoning model is constructed. By establishing the identification framework and the hierarchy of calculation factors, the comprehensive weight of calculation factors was calculated by AHP-entropy weight method; constructing the judgment matrix and using the synthesis formula to calculate the collusion intensity of the tenderee and the bidder; according to the judging standard, the bidder who have the strongest collusion with the tenderee are identified. An engineering example is used to verify the method of estimating evidence reasoning. The results show that this method is feasible and reasonable.