The utility model provides a control circuit for improving RS485 bus data transmission reliability which the characteristics are to include: main chip U1, by main chip U1 control, the RS485 communication interface's that constitutes by resistance R50, optoelectronic coupler IC3 and resistance R65 messenger's ability, transmitting circuit, the RS485 communication interface's who constitutes by resistance R61, R40, R66 and optoelectronic coupler IC2 receiving circuit. Owing to adopt optoelectronic coupler and resistance cooperation, receipts that the principle of utilizing the RS485 communication realized, send out to make and to change, can effectively solve and occupy the IO resource among the prior art to and under the circumstances of high speed, big packet, the problem of reliable data transmission. Has simple structure, data transmission rate height, good reliability, noiseless, bit error rate low grade advantage.