The invention discloses a real-time detection and control device and method for a slit width image of a carbon dioxide laser cut die plate. The device comprises an auxiliary light source assembly disposed at the lower end of a laser cutting head and a rangefinder optical lens assembly disposed on one side of the laser cutting head, wherein the auxiliary light source assembly comprises a support and three auxiliary light sources; the support is fixedly connected to the lower end of the laser cutting head, the three auxiliary light sources are fixedly connected to the support and distributed equidistantly, and the intersection point of emergent light of the three auxiliary light sources is disposed at a cutting point; the rangefinder optical lens assembly comprises an upper camera support, a lower camera support, a camera carrier, a charge coupled device (CCD) camera, a light filter and an industrial telecentric lens. The real-time detection and control device and method are used for achieving efficient, automatic and accurate detection and control and the like of the slit width of the carbon dioxide laser cut die plate; besides, the device is low in cost, small and exquisite in structure, convenient to mount and easy to operate.