Tin oxide (SnO2) has versatile applications in a variety of areas. It also shows ability to improve the flame retardancy of flexible poly(vinyl chloride) (fPVC) composite and substitute the conventional toxic flame retardant-antimony trioxide (Sb2O3). However, low flame retardant efficiency and ruined thermal stability of the PVC composite in presence of SnO2 remain to be the most prominent challenges. To address these issues, in this study, hematite (α-Fe2O3) zero-dimensional nanoparticles elaborately encapsulated SnO2 one-dimensional nanorod assemblies and such nanocasting facilitated the formation of hierarchical porosity in favor of high specific surface area and pore volume. The hierarchically nanoporous hybrid was synthesized via a facile and fast bottom-up method in a large scale and all-sided characterization was conducted on the investigation of its structure and fPVC compositions. The extra benefits imparted by α-Fe2O3 in the hybrid improved the flame retardancy of fPVC composite strikingly with reduced amount of harmful HCl gas and suppressed smoke production, without deterioration of thermal stability and mechanical property, showing much better performance than those of Sb2O3-based fPVC composite. It indicated that this new eco-friendly nanohybrid had a great potential to totally replace antimonial additive. It is expected to pave the pathway about the construction of neoteric porous hybrid nanostructures and open a new avenue to develop high performance nanocomposites.