The invention relates to a device and a method for protecting a water hammer. The device is characterized by comprising a vortex cavity and a first pipeline, wherein the first pipeline leads to the downstream position through the periphery of the vortex cavity, and a second pipeline which leads to the upstream position is arranged in the axial direction of the vortex cavity. The key points of themethod are as follows: 1. the device for protecting the water hammer is provided with the vortex cavity and the first pipeline which leads to the downstream position through the periphery of the vortex cavity, and the second pipeline which leads to the upstream position and which is arranged in the axial direction of the vortex cavity; 2. the second pipeline is communicated with an upstream pipeline; and 3. the first pipeline is communicated with a downstream pipeline. The device for protecting the water hammer has the advantages of simple structure, no need of external force, safety, reliability, no moving elements, no need of maintenance and low cost. The invention solves the defect of low reliability of the operating equipment in the traditional process of protecting the water hammer.