Abstract: In this paper the transient process during a normal pulsed Nd-glass laser beam irradiating Lyl2 aluminum targets 2mm think was observed by means of high speed schlieren framing technique. It is shown that the flow field configuration consists of expanding vapor plume, air blast wave , ejection of melted target substance and target ablation and penetration. Expanding velocity of the vapor plume of 150-190m/s, velocity of the air blast wave of 450-500m/s and velocity of the high pressure steam near the target surface of 5- 7.8km/s , are obtained, respectively, by scanning the photographs.