The invention relates to a local area network interface model, and specifically relates to an assistant selection local area network interface system and a communication method thereof. The system comprises a hardware module and a software module, and one host can establish communication links with a plurality of slaves via the system of the invention; the hardware module comprises a communication bus and a plurality of auxiliary I/O interface modules which are corresponding to the plurality of slaves one to one; hardware of the communication bus comprises a level conversion chip and a corresponding matching resistor; software of the communication bus comprises a transmitting and receiving program unit using a UART (Universal Asynchronous Receiver/Transmitter); the auxiliary I/O interface modules comprise I/O interface lines; and the software module comprises a communication time slot timer and a communication fault counter. The system provided by the invention and the communication method established based on the system have better compatibility and stability in the actual running process.