Abstract: A new ray tracing method based on Level Set method and finite difference model was proposed to calculate the laser density distribution of the keyhole wall during the transient keyhole evolution process of deep penetration laser welding.The multiple reflections Fresnel absorption of the keyhole wall and the inverse bremsstrahlung absorption of the vapor plume/plasma were simultaneously considered in this new method. The results demonstrate that the presented method can be used to calculate the laser density distribution of arbitrarily shaped keyhole accurately.