The invention discloses an adjustable water hammer protection device of a water conveying pipeline. The adjustable water hammer protection device comprises a pressure adjusting container communicatingwith the top face of the water conveying pipeline, and further comprises a sealing hole, a plug, a floating part, strip-shaped connecting parts and supporting parts. The sealing hole divides the pressure adjusting container into an upper container and a lower container. The plug is located in the lower container, and the upper surface of the plug cooperates with the sealing hole. The floating part is located in the upper container. The strip-shaped connecting parts penetrate the sealing hole to connect the floating part with the plug, so that when the water level ascends, the plug is driven by the floating part to ascend to block the sealing hole, and the highest pressure adjusting water level is controlled by changing the length of the strip-shaped connecting parts. The supporting partsare arranged in the upper container and used for blocking the floating part descending to be close to the sealing hole so as to prevent the sealing hole from being blocked. Compared with a common pressure adjusting well, in the adjustable water hammer protection device, the pressure adjusting action range can be designed and controlled, the highest water level can be limited, pipes are buried forunderground portions needing pressure adjusting, protection can be carried out when the surface elevation is lower than a normal operation water head, and overflow can be avoided.