In the permanent magnet dc motor, it is generally believed that the locked-rotor torque motor TD is Tst starting torque of the motor, but detailed analysis, there is a difference. Locked-rotor torque of the motor should be by applying a torque motor, the torque increase gradually, eventually make the motor to stop operation, the motor output torque and plus equals the braking torque, the torque can be thought of as the locked-rotor torque of the machine. At this moment motor need current is blocked current, ID = U/R, R is the internal resistance of the machine.