We evaluate the influence of water spray′s flow rates on the rate,the efficiency of laser-hard tissue ablation and the resulting surface morphology. Fresh bovine shank bone in vitro was used in the experiment. Light emitted from a pulsed CO2 laser with a wavelength of 10.64 μm and a repetition rate of 60 Hz was transmitted through an articulated-mirror-arm system and focused to a spot of which the diameter is about 400 μm on the bone sample surface directly. The radiant energy density was 26.5 J/cm2 and irradiation time was 10 s. A water spray system applied spray on sample surface with an angle of 45°during irradiation at flow rates of 0(without a water spray),0.26,0.5,0.6,0.7 and 0.9 mL/s. After irradiation,the morphological changes and microstructure of ablation craters were examined by stereoscopic microscope and scanning electron microscope (SEM) respectively. The ablation depth was also measured by optical coherence tomography (OCT). The result shows that the water spray has a profoundly influence on laser ablation rate and efficiency for hard tissue removal and the resulting morphology. Water spray not only can cool the tissue and reduce the thermal damage,but also can augment ablation rate and efficiency,and alter the surface morphology by optimal selection of laser irradiation parameters and water spray flow rate.