The steep fringing reefs are mainly formed from plate tectonics and coral growth, with coral rock on the surface layer. These topographic features greatly influence the wave propagation and wave overtopping on steep fringing reefs. However, these effects are practically ignored since only few studies focus on them. In this paper, the impact of of bottom roughness on waves overtopping over dikes on steep fringing reefs are investigated by a physical model. A series of experiments, including 72 tests of complex hydrological dynamics processes, is elaborated with three different slopes, a combination of three water depths and two bottom roughnesses. The results show that the bottom roughness signifi-cantly influences the wave propagation process and wave overtopping over the dikes on steep fringing reefs. The lower water depth on the flat reef leads to the greater of bottom effects. As a result, the discharge of wave overtopping is 35% larger when taking into account the effect of bottom roughness.