The model of 2-D unstable light field during the interaction between laser and skin-tissue was established,and the transient light distribution of tissue by Gauss and flat-top laser was calculated with diffusion approximation technique and Green′s function technique.Taking skin-tissue irradiated by He-Ne laser as an example,the skin light distribution was calculated and analyzed.The calculation shows that the light distribution in the radial direction was similar to light intensity distribution of the incident laser;light effect of skin-tissue irradiated by laser depend on laser parameters to a great extent,and power and beam size are more important.