A communication system, and a construction method and a communication method thereof are provided. The communication system includes a relay server and a plurality of communication nodes. The relay server is in signal connection with the plurality of communication nodes, the plurality of communication nodes respectively store routing links for connection to the relay server, and the relay server stores routing links respectively corresponding to the plurality of communication nodes. The plurality of communication nodes are in signal connection with a plurality of groups of terminals in one-to-one correspondence. The relay server provides communication connections for terminals connected to different communication nodes.