Abstract: Quality of Service (QoS) describes the ability of a service meeting customer needs．In a dynamic,open and diverse network environments,the QoS uncertainty makes a large deviation between the service selection results and the actual results,as well as the difficulty of guaranteeing the QoS．To solve this problem,a Web service discovery model was designed to support QoS difference control．In this model,we added the third party monitoring which is called Interceptor to ensure the reality of the QoS certification center’s information provided by service providers and customers,and its real credit data to service registry center．Also,as a notary,it ensures both sides comply with SLA fairly and justly,and ensures the legitimate transaction service．Furthermore,QoS attribute local compliance verification mechanism and the global compliance verification mechanism were added in the service user terminal and QoS certification center,to control the difference between the users’ required values and offering data by providers,making a more accurate and objective reputation from service and service providers in the transaction process．The experiment indicates that this method can effectively control the QoS difference,which can provide more satisfying Web service for the users.

Key words: Web service,QoS,Compliance,Verity,Reputation