Currently widespread in new urban projects, green roofs have shown a positive impact on urban runoff at the building scale, that is, decreased and slow peak discharge and decreases runoff volume. The aim was to study the possible impact of green roof at the catchment scale, more compatible with stormwater management issues. For this purpose, a distributed rainfall-runoff model (Multi-Hydro) devoted to urban environment and able to simulate the hydrological behaviour of green roof has been used to assess the green roof impact at such a scale. It has been applied on an urban catchment (Loup basin located in the Seine-Saint-Denis county, East of Paris, France) where most of the building roofs are flat and assumed to easily accept the implementation of green roof. Catchment responses to several rainfall events covering a wide range of meteorological situation have been simulated. The simulation results show that green roof can significantly reduce runoff volume and the magnitude of peak discharge (up to 80%) depending on the rainfall event and the initial saturation of the substrate.