Chain conveyor systems are widely used for transportation of work pieces, packages or the other goods in the industry. They are made of the drive unit, chain, section profile, return unit and racks. The trajectories of section profiles can be straight, horizontally or vertically curved. Depending on the applications, chain conveyor systems are operated with different layouts, and their chains are up to hundred meters long, and composed of a large amount of pinned single modules. The problem is that the unexpected longitudinal vibration occurs for some of their layouts. Surprisingly, almost no reference is made to this phenomenon, and no dynamic simulation is carried out to study systems on such scale in the literature. In this paper, the authors present the models of chain conveyor systems in a reduced fashion due to the large dimension of equation systems (each single chain module accounts for 2 differential equations, a 50 meter-long chain has 1500 components). Measurement results are compared with the simulation results. Parameter studies are performed by the numerical simulation. Causes of vibrations are analyzed closely. Finally, possible techniques are proposed for preventing such vibration.