Network isolation is a new solution for network security. It can protect inner network more efficiently from intrusion. In network isolation system, a high-performance communication platform is necessary for building the entire security architecture. In this paper, we mainly utilize application proxy and its differentiated services (DS) to achieve it. Firstly, we research the architecture of network isolation system and present a suitable proxy model by applying I/O multiplexing technique. And then, we present a feasible realization method of the proxy by using epoll in the proxy sub-system, whilst we illustrate the realization process in detail. Furthermore, we research QoS of the sub-system and present a realization method of its DS. At last, we research configuration and management of the system.