In order to study the optical clearing effect on reducing the skin scattering and increasing the laser energy reaching the target vessel, a quantitative study on the optical clearing effect of glycerol on the skin tissue phantom was conducted in the visible to infrared wavelength band. An in vitro experimental system for laser treatment of port wine stain was set up to obtain quantitative relationship between optical clearing effect and the blood coagulation properties under the irradiation of multi-pulse Nd∶YAG laser. The results show that the diffuse reflectance of the skin tissue phantom decreases by 36.69% and the transmittance increases by 38.73% at 1064 nm after 0.5 mL anhydrous glycerol is applied on the skin phantom surface for 10 min. After 0.5 mL anhydrous glycerol is applied on the skin tissue phantom surface for 4 min, the number of laser pulses required for blood coagulation decreases by 25%. After application for 10 min, the number of laser pulses required for blood coagulation does not decrease further, but the blood coagulation area increases by 34.1% compared with that after 4 min. The results indicate that glycerol is effective to improve the laser treatment of port wine stain by increasing the laser energy reaching the target vessel.