nm laser beam of 0.1 cm radius delivery into blood which sandwiched between two glass slides was studied by using Monte Carlo method.The dependence of diffuse reflectance and total transmittance on blood thickness,and at different blood thickness diffuse reflectance and total transmittance as a function of radius were all discussed and analyzed in detail.It showed that,diffuse reflectance of blood was very small,and it came to stabilization when the thickness of blood was thicker than 0.08 cm;total transmittance decreased with the increasing of blood thickness,and it was nearly zero when the thickness of blood was thicker than 0.10 cm;diffuse reflectance and total transmittance as a function of radius were mainly distributed in the scope of Gauss beam radius.