Abstract: An active-passive composite vision sensing system was designed to overcome the delay of active vision sensing and limited information on passive vision sensing. To capture the high brightness molten pool and low brightness structured light clearly in one image, a regional dimming method was proposed to make their brightness decline to the same level. Lightpath analysis showed that the regional dimming filter must be placed in front of the focal point before the lens, or between the CCD sensor and the focal point behind the lens. The molten pool and structured light have been clearly presented in one image using this system. An image processing algorithm for online measurement of bead geometries is proposed. The experimental results showed that the measurement error of bead height is less than 0.1 mm, and that of bead width is less than 0.2 mm.