Polymers of intrinsic microporosity (PIMs) have broad application prospects in the detoxification of chemical warfare agents (CWAs) due to their unique pore structure, good tunable reactivity, and solution processability. However, its pore structure is relatively homogeneous, resulting in high resistance to mass transfer. Here, inspired by fractal structure in nature, a structure engineering strategy is proposed to develop 3D reactive nanofibrous aerogels featuring hierarchical porous structures to minimize mass transfer resistance. These aerogels are fabricated with amidoxime-modified PIM-1 (AO-PIM-1) nanofibers serving as building units and flexible SiO₂ nanofibers acting as reinforcement. The macro/mesopores of amidoxime-modified PIM-1 nanofibrous aerogels (APAs) originating from freeze-shaping and electrospinning provide interconnected channels for the diffusion of CWAs, and the intrinsic micropores of AO-PIM-1 can effectively trap and anchor adsorbate molecules. In addition, the reactivity of the APAs can be activated by chlorine bleaching. This process forms an N-chlorine structure, which effectively oxidizes the adsorbed CWAs simulant 2-chloroethyl ethyl sulfide (CEES) by APAs, converting them into non-toxic products. The resulting aerogels have the properties of ultralight weight (8 mg cm⁻³), reversible compression strain of 60%, and repeatable sulfur mustard decontamination (half-life of 1.27 min). These characteristics indicate significant potential for the use in protective materials against vesicant CWAs.