With the purpose of investigating the millimeter order hole's formation and the drilling speed drilled by a single millisecond pulse laser, the shapes of holes in an aluminium slab drilled by a Nd: YAG Gaussian laser with 1 ms pulse width were obtained with the cutting method in an experiment. The hole depth is 1.849 mm and 2.975 mm when the laser energy is 7.9 J and 28.9 J, respectively. A semi-infinite axisymmetric model was established according to the experiment and the analytical solution of temperature in a solid phase was derived based on the thermal conduction equation. Meanwhile, by assuming that material was removed from the hole once it was melted, the function describing the hole's shape was obtained with the energy balance theory. It was found that the difference between the calculation and the experimental results becomes larger as well as the hole's depth increases with the increase of laser energy. Further investigation indicates that the variation of beam radius affects the hole's depth greatly under other unaltered conditions. Thus, the defocusing effect was induced to modify the analytical solution and obtained results are in agreemeat well with those of the experiments. Finally, the drilling speed of millisecond pulsed laser for aluminum, copper, silver and titanium were studied. The results show that drilling speed for titanium is the fastest one due to its high absorptivity for laser and poor heat conduction ability.