Mezzanine rack builds double-layer or multi-layer steel mezzanine platforms based on existing floor racks or factory ground to expand vertical storage space upward and greatly increase warehouse capacity. The ground floor can store heavy pallet goods, while the upper mezzanine is used for manual sorting and small goods stacking, equipped with special stairs and protective guardrails for anti-slip safety. It fits warehouses with sufficient factory height requiring layered storage of heavy and light goods, commonly used in hardware, auto parts and e-commerce storage.