A regulating valve used for accurately positioning a valve plug and regulating pressure or flow rate of fluid in a fluid transportation pipeline is especially suitable for power station, petroleum and chemical department, belonging to the field of engineering elements or parts. The regulating valve comprises three parts which are a valve body, a driving cylinder and a servo mechanism, and the valve body having the conventional structure of a stop valve is combined with the driving cylinder that is internally provided with a piston into a whole; a channel used for drawing in the controlled fluid is also processed; the servo mechanism mainly includes a servo pipe and a screw gearing pair (or a pinion and rack gearing pair). The gap between the end surface of the servo pipe and the end surface of an axial aerial drainage hole in the center of the piston is regulated to change the differential pressure of the controlled fluid at the two sides of the piston, and the valve plug linked with the piston is further moved and is accurately balanced at the requested position. The regulating valve has the advantages that the mobile servo pipe has low power consumption (watt level), high positioning accuracy, large turndown ratio, high sensitivity, good stability and easy combination with a fluid control system having high intelligence.