CORBA is a new generation of the distributed computing platform based on the distributed object computing technology, and security is always a fundamental problem of a distributed computing platform. Thus, implementation of security service in the CORBA platform is very important. Referring to the related security standards and distributed computing platform's security models, the CORBA security service in this paper is designed and implemented conforming to the CORBA Security Service Specification (v1.0). In addition, the necessity of supporting object invocation monitor in ORB is proposed based on our work on the CORBA security service.