The present invention discloses a control device and method for formation of a weld seam based on frontal visual sensing of a weld pool. In the present disclosure, structural light is adopted to irradiate the concave surface of the weld pool, and a visual sensor is adopted to acquire corresponding structured light images. The weld pool depression feature is acquired through image processing. The welding current is adjusted in real time to maintain the weld pool depression feature constant, and thus the uniform backside width of the weld seam can be acquired to achieve uniform and consistent penetration of the weld seam. The present disclosure only relies on the structural light information on the topside of the weld pool to achieve the control of formation of the weld seam and can be applied to the filler-wire-free DC gas tungsten arc welding of tight butt joints.