Si/graphite composite (Si/G) anodes are now regarded among the most commercially available next-generation anode materials. The development of a fully coupled mechanical-electrochemical model for Si/G anode is an essential tool to design safer and lightweight lithium-ion battery modules/packs. In this paper, we establish an efficient model to study lithium-ion battery (LIB) with Si/G composite anode through the coupling of stress-induced battery model and homogenized mechanical model. By designing strategies for the coupling of mechanical and electrochemical governing equations, a multiphysics model is proposed. Experiments for battery charging with simultaneous various mechanical loadings are conducted to validate the established model. Finally, design-oriented parametric studies for governing factors (e.g., the Si/G mixture ratio and battery size) are discussed. Results provide a fundamental understanding of the failure mechanism of the composite anode and offer a powerful design tool for Si/G composite anode design for better electrochemical performance.