For optical micro- machinery processing, nanosecond laser possess a special advantage in using it as a fabrication method of smaller hole subjected to the minimum thermal distortion. Thus it has become an effective and powerful tool widely used in drilling, cutting and welding process for micro-manufacturing field. To estimate the working performance of pulsed laser, an auxiliary method in numerical skill or semi-empirical technology is usually utilized, where the important parameters including energy intensity, duration and wavelength of laser beam will be taken into account. Nevertheless, several troubles, the unstable numerical iteration for phase change and precise calibration of sensor required in the measuring process, seem to be still inevitable, and which easily makes the numerical calculation become more complicated, even the global ablating behavior will be lost. To compensate the inadequacy mentioned above, an analytic model of optical ablation for pulsed laser, based on the evaporation effect responsible for penetration mechanism, is then derived in this study. Here the penetrating behavior, during the micro-machining process, can be clearly examined with the consideration of plasma absorption. After compared with experimental results made by Chen and Schmidt for copper drilling and steel ablation for Tim, a better agreement of analytic results identifies the accessibility of proposed model which also contributes to the future investigation on pico-or femto- laser material processing.