Grid computing is a dynamic system and trust changes over time. A kind of flexible trust management is urgently required that could obtain new, not foreseen trust value by computing or reasoning. Semantic grid makes it easier for resources to be discovered and joined up automatically. But there are not explicit semantic content for trust management. By taking full advantage of the content of semantic grid service, trust content model and content-included trust statement model are designed in this paper. In order to obtaining new trust value by the content of trust semantic and grid service semantic information, semTrustStatement ontology, service content model, context model, situation model are defined and the influence relationship between them are shown. At last an example is taken verifying the method valid.