The influence of various parameter changes of the vertical air vessel in the long-distance water conveyance system on its water hammer protection ability is analyzed and discussed. By taking a water supply project as an example， the Extended Fourier Amplitude Test （EFAST） method is used. The maximum positive pressure， the minimum negative pressure and the maximum reversing speed of the pump in the accidental pumping condition are taken as the results of the air vessel water hammer protection. An analysis of the parameter is based on the global sensitivity of the air vessel water hammer protection effect when the reference value is ±50%. The results show that the main parameters that affect the maximum water hammer pressure of the air vessel are the diameter of the connecting pipe， the volume of the air vessel and the gas-liquid ratio； the main parameters that affect the lowest negative pressure are the diameter of the connecting pipe， the outlet local resistance coefficient， the gas-liquid ratio and the length of the connecting pipe. The main parameters that affect the maximum reversing speed of the pump are the diameter of the connecting pipe， the gas-liquid ratio and the volume of the air vessel in order. Among them， the diameter of the connecting pipe between the air vessel and the main pipe is the most sensitive parameter that affects the maximum pressure， the minimum negative pressure and the maximum reverse speed of the pump.