Objective Under different tensions, the paper lateral and vertical diffusions of the 4-color printing were analyzed. The relationships between the printing tension and the register offset were obtained. Then the best printing tension range in printing practice was obtained, which can guide the actual printing. Methods The register marks were set in the specified position of the 4-color plates to detect the paper deformation. The printing process was operated under different tensions. Using CCD camera and image processing techniques, the image of register marks on the printed paper was picked, processed and analyzed to obtain the relationship curves between the lateral diffusions, vertical diffusions and printing tensions. Results The experimental results and curves were matched with the theoretical analysis. The experiment and research methods can be used as an effective method of production and quality management. Conclusion In web printing, when the tension was small , the lateral and vertical register offsets maintained a linear relationship with the tension. As the tension increased, the lateral diffusion and the vertical position tended to decrease and then became stable. When the tension exceeded a critical value, the effect of the tension change on the register offset was smaller, which is suitable for printing offset compensation and control.