Abstract: To address the issues of poor wet stability and limited interfacial active sites in traditional cellulose-based foams, this study proposes a novel strategy to construct polydopamine/pulp fiber (PDA/PF) composite foams via ambient pressure drying. The composite foams were fabricated through mechanical foaming, combined with Ca²⁺ crosslinking and ambient pressure drying, and the processing conditions were optimized via orthogonal experiments. Subsequently, an in-situ polydopamine polymerization technique was employed to construct a functional layer on the foam skeleton. The composite foams were systematically characterized in terms of microstructure, chemical structure, mechanical strength, and filtration performance toward microplastics. The results demonstrated that the composite foams form a stable three-dimensional porous network under ambient pressure drying. PDA effectively enhanced interfacial adhesion between fibers, significantly improving the wet-state mechanical stability and deformation recovery ability of the foams, with the pure water flux reaching 18000 L⋅m⁻²⋅h⁻¹. Meanwhile, the composite foams exhibited a removal efficiency of 92% toward positively charged polystyrene microplastics (PS-NH₂), and the removal rate remained above 90% after 10 consecutive filtration cycles. In summary, the proposed strategy of preparing PDA/PF composite foams via ambient pressure drying provides new insights for the development of high-performance cellulose-based filtration materials.