A method for remotely shutting down a downhole unit of a rotary steering system from ground includes steps of: a: calculating a pressure difference P1 between a front end and a rear end of the drill water hole; b: calculating an extension loss ΔP; c: calculating a pressure P2 at the riser after turning on the downlink device; d: calculating an opening area S1 of the throttle valve of the downlink device; and e: adjusting the throttle valve to a calculated opening degree; automatically targeting the function block that needs to be cut off according to a flow change detected downhole, and shutting down the downhole unit. The method can realize self-protection and continuous operation of the entire rotary steering system, reduce frequency of inspection that needs to pull back the drill when the rotary steering system is abnormal, improve drilling efficiency, and reduce costs.