Renewable biomass-based activated carbon fiber paper (ACFP) possesses a three-dimensional network porous structure for high-efficient toxic gas purification. However, intelligently building high catalytic activity biomass-based carbon materials with superior flexibility remains a significant challenge. Herein, a series of paper-based catalysts (MnO2/ACFP) with varying MnO2 loadings were fabricated by combining MnO2-loaded ACF and softwood (Pinales) fiber via a wet-papermaking process. The precursor derives from abundant and green biomass, meanwhile, the channels of plant fiber facilitate gas flow and the effective dispersion of active sites. Noteworthy, the introduction of softwood fiber imparts flexibility to the catalyst, enabling it to be folded, wound, and bent without compromising mechanical strength, thus exhibiting excellent processability. Formaldehyde (HCHO) removal in a static system was applied to evaluate their reactivities. Among all, MnO2/ACFP-1.7 (12.22 wt% Mn) shows 100 % removal of HCHO in 1 h with a turnover frequency value of 0.01526 min−1, being more than 10 times that of the bulk MnO2 particles. The underlying mechanism for the enhanced catalytic performance can be ascribed to the synergistic effect of its stronger gas capture ability together with more exposed active sites. This work provides insight into the design of a flexible and environmentally friendly catalyst for the degradation of organic contaminants.