Objective In OCR system, image preprocessing is particularly important for recognition of unlimited handwritten Chinese characters. Some unavoidable factors from image background, image skew and touching characters bring in errors for character segmentation, recognition and post-processing. In this paper, we focused on the image preprocessing method for recognition of handwritten Chinese characters in EMS Forms and the whole process was shown. Methods Method of finding fitting Straight Line by Least Squares was used to deal with the relocation and segmentation of the target image. Block threshold based Otsu's method was adopted to remove the image background and to eliminate the noise interferences. Results The proposed method was tested on 1024 real EMS envelope images. The system achieved a recognition rate of 86.3% . Conclusion The experimental results demonstrated that the proposed method effectively reduced the influence of image noises on the segmentation and recognition of handwritten Chinese characters.