The image ink of printed document is composed of halftone dot ink. Different manufacturers have confgured different halftone algorithms for printing equipment, which makes the printed image have specific dot morphology. Two-dimensional fast Fourier transform (FFT) technology can transform the printed dot image from spatial domain to frequency domain, and obtain the spectral characteristics of dot ink. Therefore, spectral analysis can effective ly assist in identifying the formation mode of the document. This paper selects 27 kinds of 32 toner printing equipment that are common in the market, and samples and analyzes the ink spectrum characteristics of images printed and copied by toner multifunctional printing equipment, focusing on the analysis of the ink spectrum characteristics of amplitude-modulated screen printing images, blue noise screen copying images and images with two sets of dots superimposed by copying and printing originals. The results show that two-dimensional FFT provides easy-to-identify ink spectrum characteristics, which can distinguish the ink morphology of images printed by different halftone algorithms, thus distinguishing between copied and printed images, and at the same time identifying the formation mode of copied manuscripts. In this paper, a method based on FFT technology is proposed to identify the ink formation mode of toner printing documents, which provides an objective and effective new method and basis for judging the document formation mode in document retrieval.