This paper aims to study the influence of the radial runout of the embossing cylinder on the printing pressure and dot deformation, so as to provide a reference basis for reducing the dot gain rate and improving the print quality in flexographic printing. This paper built an analysis model of maximum printing pressure in flexographic through using the basic theory of contact mechanics to analyze the contact state between the impression cylinder and the plate cylinder, taking flexographic as an example. An analysis model for the dot gain rate because of the impression cylinder run-out in flexographic plate was built by using the Finite Element Method to analyze the relationship between the printing pressure and the dot deformation on flexographic plate, building. Combining with actual measurement of the impression cylinder radial run-out waveform and the analysis model of pressure and dot gain rate in flexographic, it can be conclude that:The amount of compression need to be accurately controlled as the increase of the maximum printing pressure will increase the top dot area and the dot gain rate; The radial run-out of the impression cylinder will change the actual amount of compression, which makes the maximum printing pressure fluctuate during printing in flexographic; When the pressing amount is 0.1mm, the radial runout is −0.053 99~0.054 48mm, the number of lines is 69 lines/cm, the printing plate with 50% dots, and the dot gain rate fluctuates between 3.639%~9.526% The radial runout of the embossing cylinder changes the actual pressure between the cylinders, causes the change of the printing pressure, and causes different deformation of the dot, which seriously affects the printing quality.