The invention relates to a communication server, in particular to a server for communication connection between PC and PLC, which comprises a server interface module, a communication connection interface module, a server operational module, an equipment module, a protocol module and a delivery module, wherein the server interface module provides server parameter configuration and delivers communication request messages; the communication connection interface module provides a function interface for the communication connection in the server; the server operational module is the core module of the server in running; the equipment module provides physical equipment support for the server; the protocol module provides protocol support for the server; and the delivery module processes modules which deliver communication requests according to protocol requirements used by the communication requests. The invention has the advantages of low development and maintenance cost and high expandability and can simultaneously provide support for a plurality of application programs.