The invention discloses a pump-stopping water hammer protection method and a pump-stopping water hammer protection device for a centrifugal pump. According to the pump-stopping water hammer protection method for the centrifugal pump, a water pump spindle of a water pump unit and/or a motor spindle are designed into a structure mode of two-end shaft extension, the outer-side shaft extension end of the water pump spindle and/or the motor spindle are connected with an electromagnetic clutch, and the rear end of the electromagnetic clutch is connected with an inertia fly wheel. When the water pump unit works, the electromagnetic clutch is separated. When the water pump unit is in power failure to stop a pump, the electromagnetic clutch is combined and applies inertia moment to the water pump unit and/or a motor to increase rotational inertia through the inertia fly wheel, and thus the water hammer protection is realized. When the centrifugal pump stops, the device can immediately apply the inertia moment to increase the rotational inertia, and therefore the time when the water pump unit starts to inversely rotate is prolonged, the speed of inverse rotation of the water pump is reduced within rated rotation speed, the water hammer pressure in a pipeline is reduced, and the purpose of pump-stopping water hammer protection is achieved. Moreover, the motor load is not increased, energy consumption is not increased, the engineering investment can be effectively reduced, and the water delivery cost is reduced.