The utility model relates to a nonpolarity RS485 protects adapter circuit, it includes surge protection circuit and RS485 protection circuit, the one -level protection circuit that comprises ceramic discharge tube in the setting of surge protection circuit part and constitutes the second grade protection circuit with static surge suppressor TVS by the self -resuming fuse can absorb big surge and release, plays the lightning protection effect, protects the rear end circuit, set up pull -up resistance and pull down resistor in RS485 protection circuit part, use with at 485 chips of heteropolarity and 485 nonpolarity chips and use under the condition, charge or discharge through diode pair electric capacity, become 485 chips of heteropolarity with 485 nonpolarity chips, reach the effect to RS485 line protection.