Silicon is a promising active material for lithium ion battery anode, because of its high theoretical specific capacity. However, due to the significant volume change during the operating cycles, the practical applications of silicon-based anode are restricted. Delamination of the silicon layer from the current collector substrate is one of the major failure modes; and its effects on the performances of Si anode need to be better understood. In this study, a multiphysics based finite element model is established to investigate the impact of Si layer delamination on the capacity degradation of the Si anode. It is found that depth of delamination, Si layer thickness, and charging/discharging C-rate are three critical influencing factors for the performances of the Si anode. With the increase of depth of delamination and Si layer thickness, the remaining useful capacity of the Si anode will gradually reduce. In addition, under high C-rate operating conditions, the capacity loss of the anode will be largely exaggerated by the presence of the delamination.