Trustworthiness plays an important role in service selection and usage. However, it is not easy to define and compute the service trustworthiness because of its subject meaning and also the different views on it. In this paper, we describe the meaning of trustworthiness and the computation method for trustworthiness fusion. Through extracting trustworthiness from service provider, service requestor and service broker, we creatively adopted D-S (Dempster-Shafer) evident theory to fuse the tripartite trustworthiness. Finally, we completed some comparison experiments on our web service supermarket platform and certified the efficiency of our method.