The modular data center networks comprise inter-and intra-module networks. The structure and routing of inter-module networks take charge of organizing modules, and communicating among servers in different modules. Thus, it is the most important issue to design an inter-module structure with high bandwidth, high fault-tolerance, and flexible scalability to build the mega-modular data center. In this paper, an inter-module network structure called MDKautz is proposed for building the mega-modular data center. MDKautz uses Kautz as the basic interconnection topology among modules, and builds the mega-modular data center network with high bandwidth, high fault tolerance and good scalability without the need of any additional high end switches. The method for how to constructing, routing and expanding in MDKautz are analyzed. Mathematical analysis and experiment results show that MDKautz has a good topology characteristic and communication performance, and can effectively support the typical applications with high bandwidth and high fault tolerance in data center.