Abstract: Based on the metal melt and vaporized interface 2D propagation mechanism, this paper founds the pulsed laser welding model. This model divides the interactive zone and pulse duration in to many units, which is used for weld profile calculation. We put forw ard the intensity redistribution mechanism in keyhole cavity to exposit the weld seam cross section profile preciously. This intensity redistribution mechanism in keyhole cavity mainly take up the Frenel preciously at cavity wall, and the in tensity superimposition is attributed to noncoherent superimposition, which is independent on the incident angle. The local unit after every reflection is decided by ray trace method. This model gives out the weld profile along with the laser pulse power P, focus diameter a, absorptance α, and the profile curve variation vs the interactive time t. The theory results show that the weld seam cross section profile is influenced significantly by laser pulse power, focus diameter and pulse duration. This is correspondent to actual weld situations. Meanwhile, the theory results can explain the weld cross section curve zigzagged characteristics.