Abstract: This papaer advanced that the client/server model of process is the bes t model for heterogeneous PLC communication service software on industrial Ether net in accordance with its special characteristics, and proposed an ideal of se amless connection between heterogeneous PLC networks in control systems by invok ing API function based on the model. The key technique used in communication ser ve software were analyzed in detail. Through the analysis of the program, the scienti fic practicability of the method is verified.