The invention discloses a method and a system for dynamically extracting key information of express sheets. The method includes collecting image data by a camera, subjecting images to a Wiener filtering algorithm, restoring degraded images, subjecting the images to binarization processing and erosion and dilation processing, locating target areas of the key information according to image structure features of the express sheets, subjecting the images to rotation transformation and cutting to facilitate subsequent recognition, realizing information separation through a seed filling algorithm, and realizing information recognition through a pattern recognition algorithm. The method is capable of improving sorting efficiency of the logistics industry and reducing labor cost.