Free-running holmium∶YAG lasers transmitting in a fiber with core diameter of 800 mm can induce vaporization bubble explosively at the end of fiber underwater. Shock waves will be produced upon the vaporization bubble collapse. The shape and dynamic state of vaporization bubble under different laser parameters, can result in variable parameters of the number, intensity, oscillation period, acoustic frequency, and so on, of shock waves. An acoustic measurement system has been built to investigate the influence of pulse duration on acoustic transients, and the characteristic parameters of the first acoustic transient can be recorded by an oscillograph. The experimental results indicate that under the condition of 1000 V voltage, 5 Hz frequency, 0.7~1.6 ms pulse duration of pump power, resonance will happen for the intensity of acoustic transients at the starting period. Finally the intensity will decrease after reaching the peak value of 1.01 MPa. The frequency of acoustic transients will always decrease gradually as the pulse duration of lasers increases, and its peak value can reach 400 Hz. Holmium∶YAG lasers with higher energy and shorter pulse duration can induce acoustic transients with higher intensity, more number, shorter period, and higher frequency.