The services over Internet are often dynamic, evolving and growing due to the changes of the requirements and operating contexts. Therefore, it is necessary to effectively manage the dynamics of services in order to support flexible, efficient, and transparent services access for applications at run-time. This paper proposes an agent-based technical framework of managing dynamics of services, in which agent as the bridge between the applications and the target services is responsible for encapsulating the services as its behaviours, monitoring the dynamic of services, and providing proper services for applications. The situation model of services and implementation architecture of service manager are designed to specify the expected dynamic aspects of services and support the monitoring and access on services. Based on Jade and Tomcat, we have developed a prototype platform called ServiceAutoManager to implement the above technologies and studied a case to show the effectiveness of our proposed approach.