The present invention belongs to site bus technology in automatic system. The internal module connecting bus for site controlling computer includes full duplex bus and concentrator, and the full duplex bus is connected to the concentrator and server as the I/O port of the concentrator; the inputs of logic operation circuit are connected to the input of the concentrator separately and the output of logic operation circuit are connected to the outputs of the concentrator via a bus. The realization method includes the data exchange between the outer module and the concentrator performs in semi-duplex mode via the full duplex bus, coupling the input data from the modules to one bus by the concentrator, and sending the data of the modules via the bus.