Silicon is a well-known anode material for lithium-ion batteries that has attracted a lot of interests because of its high theoretical specific capacity (4200 mAh g⁻¹). However, its severe volume expansion during cycling leads to structural degradation and rapid capacity fading. The design of porous silicon architectures has emerged as a fundamental and effective strategy to mitigate these issues by accommodating mechanical stress and preserving electrode integrity. Concurrently, the development of advanced in situ/operando characterization techniques has shifted the research paradigm, enabling direct observation of dynamic structural and interfacial evolution under operating conditions. This review systematically summarizes recent progress in the rational design of porous Si-based anodes and critically examines how state-of-the-art in situ methods provide direct mechanistic validation of these designs. The work highlights the synergistic interplay between targeted material engineering and in situ/operando characterization, offering a roadmap for the development of high-performance porous silicon anodes.