The spatial laser energy absorption inside the keyhole is decisive for the dynamic molten pool behaviors and the resultant weld properties in high-power laser beam welding. In this paper, a numerical simulation of the LBW process, considering the 3D transient heat transfer, fluid flow and keyhole dynamics, is implemented, in which the free surface is tracked by the volume-of-fluid algorithm. The underlying laser-material interactions i.e., the multiple reflections and Fresnel absorption, are considered by an advanced ray-tracing method based on a localized Level-Set strategy. The laser energy absorption is analyzed from a time-averaged point of view for a better statistical representation. It is found for the first time that a noticeable drop of the time-averaged laser energy absorption occurs at the focal position of the laser beam, and the rest region of the keyhole has relatively homogenous absorbed energy. This unique absorption pattern may lead to a certain keyhole instability and have a strong correlation with the detrimental narrowing phenomenon in the molten pool. The influence of the different focal positions of the laser beam on the keyhole dynamics and weld pool profile is also analyzed and compared. The obtained numerical results are compared with experimental measurements to assure the validity of the proposed model.