Open-source 5G Core (5GC) projects are effective tools to deploy commercial 5G networks, develop 5G demonstration testbeds, and research the future mobile Core Network (CN) evolution. Open5GS is one of the most popular open-source 5GC projects, whose CN strictly follows the 3GPP standard and has been maturely developed. However, the present Open5GS can only realize basic 5GC functions thus limiting further research based on this platform. This paper presents our development work based on Open5GS. We have deployed independent 5GC in different virtual machines and upgraded some network functions of Open5GS to support the multi-node scenario simulation, i.e., different 5G networks participate in the registration and session establishment procedures of the accessed User Equipment (UE) together. Testing results show that the UE subscribed in its home network can access the serving network successfully, which means that our testbed satisfies the basic requirements of multi-node simulation. Not only as a multi-node 5GC demonstration platform, this testbed is also helpful for the in-depth study of future CN evolution.