Outcome-based contract( OBC) is a kind of contracting mechanism,which allows the customer to pay only when the firm has delivered outcomes,rather than activities and tasks involved. To achieve the higher demand of the delivering outcome of the contract,the evaluation of contractor’s performance was focused on. A reasonable and objective contractor performance evaluation system is constructed by considering various uncertainties. The set pair theory is used to analyze the four-element connection of quality of service contractors. It aims to provide a theoretical basis for the decisionmaker to make confirmation of the equipment contractor who has a better performance and development trend. Outcome-based contract (OBC) is a kind of contracting mechanism, which allows the customer to pay only when the firm has delivered outcomes, rather than activities and tasks involved. To achieve the higher demand of the delivering demand of the contract, the evaluation A reasonable and objective contractor performance evaluation system is constructed by considering various uncertainties. The set pair theory is used to analyze the four-element connection of quality of service contractors. It aims to provide a theoretical basis for the decisionmaker to make confirmation of the equipment contractor who has a better performance and development trend.