Keyhole instability is an important factor influencing defect formation in deep-penetration laser welding. This study investigates the use of 304 stainless steel as the welding material and examines the influence of spot spacing on keyhole behavior during dual-beam laser welding with a 50∶50 energy ratio. A high-speed camera was used for this intensive investigation. This study explores how a dual-beam laser source enhances keyhole stability by analyzing keyhole morphology and porosity. Results indicate that as the spot spacing increases from 0 to 1.800 mm, a single keyhole splits into two, with keyhole stability initially increasing and then decreasing. The most stable keyhole is achieved at a spot spacing of 0.450 mm, as indicated by a standard deviation in keyhole depth variation of 0.03. This improvement is mainly due to a noticeable reduction in the nonuniform evaporation of the metal liquid and an increase in the distance between the keyhole front and back walls.