The author analyzes contact and easy wearing and reliability of export signal existing in potentiometer terminal model hydraulic turbine leaf of transmit water current servomotor displacement transmission equipment. A hydraulic turbine leaf of transmit water current relay machine displacement transmission device is designed based on the principles of caoacitance sensor. The device can avoid the problem of old displacement transmission, and long time and reliably measure displacement volume of hydraulic turbine leaf of transmit water current relay machine.