After the overhaul of an extraction condensing steam turbine, the opening of intake control valve increased abnormally and the volume of extraction steam increased obviously. Through test and maintenance, it was found that the leakage of extraction check valve and the entrance of the steam from extraction pipe network into the turbine increased the pressure at the extraction nozzle, reduced the efficiency of steam turbine and caused the abnormal intake and extraction flow. The extraction check valve and its actuator were repaired, and the initial position of the check valve stem was adjusted, then the steam turbine returned to normal operation.