Laser ablation-assisted laser welding can regulate the porosity and further improve the tensile strength. In this paper, the effect of laser ablation density on the surface oxygen content and surface morphology was studied after the welding parameters were optimally selected. With 0 J/cm2, the surface oxygen content was 8.91% and the surface was flat. After laser ablation, the oxygen content first decreased and then increased. With 8.75 J/cm2, the oxygen content was 2.75%, which was only 30.86% of 0 J/cm2. A uniform crater morphology was formed. The excessive energy caused thermal oxidation and irregular ablation morphology. Quantitative analysis was performed using σa and σb as the standard deviations of the ejected plasma and molten pool fluctuations, respectively. σa and σb were 0.173 and 0.045 with 0 J/cm2. With 8.75 J/cm2, σa and σb were 0.176 and 0.049, respectively, which were closest to 0 J/cm2. With 35 J/cm2, it was the opposite. With 0 J/cm2, a large number of pores were found and the porosity was 1.85%. Three locations of pore formation under the influence of keyhole and molten pool behavior were analyzed. With 8.75 J/cm2, only a very small amount of porosity was observed, with porosity of 0.28%. The room temperature tensile strengths with 0 J/cm2 and 8.75 J/cm2 were 962.94 MPa and 1 130.47 MPa, respectively. The fracture morphology exhibited ductile fracture.