In order to resolve existing problems such as low efficiency， high cost and lack of technical resource in current maintenance， it is indispensable to realize remote diagnosis for hydroelectric generating sets（HGSs）. In this work， basing on the service-oriented architecture（SOA） and Web service technology， a SOA-oriented E-diagnosis system for HGSs（HGS-SES） is proposed and the framework of HGS-SES is then constructed; the key modules of the system are introduced; a specific diagnostic procedure and the system development example are given. The HGS-SES makes systematic information transfer rapidly and conveniently to implement service function and diagnosis decision-making， develops a dynamic network diagnostic platform for HGSs， and has promising application in the future.