In order to solve the problem of low efficiency by manual way of identification, this paper uses HALCON software as a platform to identify the invoice number. Firstly, the image preprocessing is carried out, which includes transforming the original image into single channel image, image enhancement, Gaussian filtering, threshold segmentation and connected region segmentation; Secondly, the mathematical morphology of the pretreated image is processed, And then ,the figures of the split; Finally, the number of the invoice number is identified by MLP (multilayer perceptual classifier). By comparing with the manual method, the results show that the invoice number can be quickly and accurately identified by the method based on HALCON, which can effectively reduce the workload of the staff and improve the efficiency of the work.