The invention relates to an automatic detection device and method of the geometric quality of a large-sized thin-plate metal workpiece. An overall image and a distance of a thin-plate workpiece are collected at a detection position and the collected image and distance information are transmitted to an image processing unit; the image processing unit obtains the number of processing holes and central positions of all holes, identifies arc and segment pixels, determines the pixel types and the numbers of all types of pixels, and calculates workpiece thickness information; if the hole number, theworkpiece thickness and the hole types meet requirements, a local sensing unit collected a workpiece sequence image and transmits the image to the image processing unit; the image processing unit processes a local sequence image and identifies dimension information and position information of the obtained pixels; and if the pixel dimensions and positions meet requirements, a detection result is outputted. According to the invention, the original image of a to-be-detected workpiece is collected and obtained by means of macro-micro combination and quality detection of the large-sized workpieceis realized; the detection precision is ensured; the restriction on the workpiece dimension is eliminated; and the detection range and the detection precision are improved.