Abstract: In order to select suitable protection measures for water hammer of cavities collapsing, the mathematical model of air valve under hydraulic transient condition was established according to the characteristics of long-distance gravity and pressure flow. The Bentley Haestad Hammer software was used to simulate the water hammer in a long distance water conveyance project. The results showed that the transient pressure rise are 157 m, 200.6m and 40 m respectively under the conditions of no air valve, setting compound intake and exhaust valve and water-proof hammer air valve, and the corresponding boost ratios are 3.75, 5.62 and 1.93. Under the condition of no air valve and compound air intake and exhaust valve, the water hammer of cavities collapsing had occurred, the maximum cavity volume was 350L and 775L respectively, and the waterproof hammer air valve can effectively avoid the water hammer. Under the three operating conditions, only the pressor of water-proof hammer air valve was the lowest, and the maximum pressor was 74.5% lower than that without the air valve, and the overall fluctuation was the slowest. Through comparing and analyzing the incoming and exhausting gas volume and pressure variation under three working conditions, it is known that the difference of incoming and exhausting volume between working condition 2 and working condition 3 is 2198~5558L, and the minimum pressure difference is-0.05~0.01MPa, and the maximum pressure difference is 0.38~ 0.89 MPa. In working condition 2, during the process of valve closing at the end of the pipeline, the incoming and exhausting gas volume changed violently, superimposing on the shut-off valve water hammer, while the change of incoming and exhausting volume of the valve in working condition 3 was more relaxed, which has controlled the gas volume and the peak value of water pressure effectively. It can be considered that the water-proof hammer type air valve is an effective protection measure for water hammer of cavities collapsing.