Abstract: In order to get the damage features of nanosecond laser pulse width to aluminium and provided the basis for choosing proper pulse width in the processing of metals by nanosecond laser, by using the area calculation method and instruments (optical microscope, scanning electron microscope and surface profiler), the damage thresholds of 37 kinds of nanosecond laser (pulse width of 10ns~520ns, wavelength of 1064nm) on aluminium were obtained. The effects of laser pulse number on damage thresholds of aluminium were analyzed with constant pulse width. The function mechanism of nanosecond laser pulse width on the quality of drilling holes in aluminium was also revealed. The results show that the damage threshold of single pulse is linearly related to the square root of laser pulse width of nanosecond laser. The damage threshold of aluminium decreases with the increase of the number of pulse width. The narrower the pulse width of nanosecond laser is, the higher the damage threshold to aluminium is. Evaporation process occupies the leading position during the drilling process. Furthermore, the less the melted thing on the inner wall of hole is, the better the circular degree of hole will be. The less the spraying materials in the orifice is, the higher the quality of drilling will be. The results provide the guide for choosing proper pulse width in the processing of metals with nanosecond laser.