In grid environment, there are many administrative domains, each domain has its own CA, and entities in different domains need authentication when accessing each other. The OCSP (Online Certificate Status Protocol) stands out due to its ability to carry near real time certificate status information and meet the need of grid. The paper proposes an extended OCSP protocol that can provide trust status for certificate to benefit the certificate validation between different domains. We describe the extended OCSP protocol, the realization framework and the work mechanism. An extended OCSP responder is built to verify the feasibility of the extended OCSP protocol for grid.