Two-dimensional (2D) magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices. The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism. Here, we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe₃GeTe₂ (FGT) with a thickness range of 11.2–112 nm. Three types of domain structures and their corresponding hysteresis loops can be obtained. The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness, which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields. These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness. Our finding not only enriches the fundamental magnetism, but also paves a way towards spintronics based on 2D magnet.