This paper focuses on modelling of structural response of RC cantilever beams retrofitted with a thin layer of Ultra High Performance Fibre Reinforced cement-based Composite (UHPFRC). The complex cracking phenomenon of the resulting RC-UHPFRC composite system is carried out by a numerical model incorporating the real nonlinear materials laws, in order to predict accurately the mechanical behaviour. To validate the model, experimental data obtained from RC-UHPFRC cantilever are confronted with the numerical findings. The model can predict efficiently the structural resistance of the tested composite systems. The model can be used for prediction purposes in design for real concrete structures strengthened by UHPFRC.