Recently, laser therapy has been widely used for treating portwine stain (PWS) and other vascular lesions. However, the mechanism of the vascular injury during the treatment process is still not clear. In this paper, a hamster dorsal window chamber model is constructed to investigate the dynamic change of the vessel during pulsed laser treatment. A CCD camera and microscope are used to capture the dynamic variation of microvessels after 1064 nm laser pulse exposures. Experimental results show that the vessel continues expansion with the increasing of the radiant exposure, and vasoconstriction appears when the energy accumulates to a certain value with a single laser pulse. After multiple laser pulse irradiation, vessel expansion, blood coagulation and vasoconstriction are observed. These results may provide useful feedback for the treatment of PWS by near-infrared long wave laser.