Optical coherence tomography (OCT) allows a direct and precise measurement of laser welding depth by coaxially measuring the keyhole depth and can be used for process monitoring and control. When OCT measurement was taken during single-beam laser welding, the keyhole instability of aluminum welding resulted in highly scattered OCT data and complicated the welding depth extraction methods. As a combination of an inner core beam and an outer ring beam, a novel adjustable ring mode (ARM) laser for producing stable keyhole was applied to the OCT measurement. Different ARM laser power arrangements were conducted on aluminum and copper. Results indicated that the ring beam greatly improved the stability of the core beam-induced keyhole, and smooth welding depth can be extracted from the concentrated OCT data.