Objective: This paper investigates the overall overlap, single character overlap, and partial overlap probabilities between the signature handwriting of a writing robot and that of a natural person, and investigates the specific factors affecting the overlap probabilities. Methods: Fifty sets of natural human signature handwriting were collected, facsimiles of the writing robot’s signature handwriting were prepared, and experimental samples of the robot’s signature handwriting were written using a curved-joint writing robot and a linear-joint writing robot, respectively. PHTOTSHOP software was used to compare the handwriting of the writing robot with the handwriting of natural persons. Results: The handwriting of the writing robot and the handwriting of the natural person both have different degrees of single character overlap and partial overlap, but not all handwriting can overlap with the natural person’s handwriting as a whole. Conclusion: The factors affecting the probability of overlap are not only caused by the nature of the natural person’s signature handwriting itself, but also the result of the combined effect of many factors in the robot writing process, which should be paid attention to and analyzed in research and practice.