The invention relates to a water-hammer-preventing ultrasonic water level detection method, comprising the following steps of: (1) selecting an A type pulse reflection type ultrasonic flaw detector with a work frequency range of 0.5 MHz-10 MHz; (2) selecting a probe; (3) selecting a straight pipe which is the same as a detected pipe in specification and material as a comparing test block; (4) adjusting the detection sensitivity of the ultrasonic flaw detector; (5) determining a part to be detected of a pipeline; polishing until a metal luster can be observed and coating a coupling agent; (6) placing the probe on the part to be detected of the pipeline and starting an instrument to detect; (7) comparing a wave outputting position with a detection reference reflecting wave position; and (8) if the wave outputting position is in front of a reference reflecting wave, determining that a water level is lower than a threshold value; and after the wave outputting position is behind the reference reflecting wave, determining that the water level exceeds the threshold value. The water-hammer-preventing ultrasonic water level detection method accurately judges whether the water level of the pipeline exceeds the highest allowable water level value or not so as to provide technology supports to the operation and manipulation in time and avoid a water hammer phenomenon; and the water-hammer-preventing ultrasonic water level detection method is good for safe production and operation, and reducing and avoiding personnel damages and economical losses, which are caused by the water hammer.