As for communication network simulation, embedding real network into simulation loop can bring lots of advantage. However, there are some problems waiting to be addressed. Targeting the application of communication network training, this paper firstly put forward a simulation structure of "Real-Network-in-the-Loop", which can connect the real communication network with the simulated communication network and implement the data packet interaction between two. Secondly, this paper designed the internal structure of IP/HLA Converter, which can complete the conversion between the IP-format data packet and HLA-format data packet. Finally, this paper put forward some ways for realization of key techniques such as IP packet intercepting, raw IP packet sending and etc. With above schemes, paper solved the simulation issue of "Real-Network-in-the-Loop" fully.