A serial printer sometimes generates vertical stripped patterns in the printing image, which is called jitter and is a main cause decreasing the quality of printing image. The jitter is due to the vibration of print-head carriage system. The purpose of this paper is to build up a simulation technology of the vibration of carriage system and clarify the vibration characteristics of the system. The basic motion equation of carriage system, including a carriage, a stepping motor, a couple of reduction gears, and a synchronous belt, is derived firstly. Then, the natural vibration and forced vibration of carriage system is analyzed by linearizing the basic motion equation. A velocity fluctuation ratio is induced for evaluating the vibration level of belt meshing and gear meshing. The theoretical analysis is confirmed with calculations and experiments, and the vibration of belt meshing is especially discussed in detail.