In order to enhance service survivability, an immune-based model for service survivability, referred to as ISSM, is presented. In the model, the concepts and formal definitions of self, nonself, immunocyte, diversity system, and etc., are given; the antibody concentration and the dynamic change process of host status are described. Building on the relationship between the antibody concentration and the state of an illness in the human immune system, the systemic service capability and the service risk are calculated quantitatively. Based on the differences of the immune system among individuals, a service survivability algorithm, dynamic service migration algorithm, is put forth. Simulation results show that the model is real-time and adaptive, thus providing an effective solution for service survivability.