Single-walled  carbon  nanotubes  (SWCNTs)  are  considered highly promising flexible thermoelectric  materials because of their excellent electrical transport  properties,  mechanical flexibility, and  solution processability. However, their thermoelectric performance is still limited by the difficulty of simultaneously optimizing electrical conductivity and the Seebeck coefficient. In this work, semiconducting nonmetallic carbon- and metallic iron-doped exfoliated  hexagonal  boron  nitride  nano-sheets  (BNNSs)  have  been  firstly synthesized by high temperature pyrolysis and microwave-assisted synthesis method,  respectively.  Then, the as-prepared  C(Fe)-doped  BNNSs  are  incorporated  into  SWCNT  networks  to  construct composite films with  designed  hetero-interfaces for improved thermoelectric performance. The introduction of Fe-BNNSs and C-BNNSs creats abundant heterointerfaces,  inducing  an energy-filtering effect and increasing the Seebeck coefficient. Notably, C-BNNS forms a conformal coating on SWCNTs, and C-BNNS enhances π-π interactions with SWCNTs, improving their dispersion and facilitating carrier transport. Meanwhile, the stable coated heterojunction synergistically boosts electrical conductivity and the Seebeck coefficient, further enhancing thermoelectric properties. In this system, carbon doping plays a dual role by simultaneously realizing band engineering of BNNSs and interfacial regulation within the SWCNT network, whereas iron doping mainly contributes through band structure modulation. As a result, the optimized C-BNNS/SWCNT composite film achieves a maximum power factor of 389.7 μW m^-1 K^-2. In addition, the assembled thermoelectric device delivers a normalized power density of 1.9 × 10 W m^-1 K^-2. Therefore, this work demonstrates that element-doped BNNSs serve as efficient nano-fillers to modulate charge transport behavior and interfacial properties in SWCNT films, which offers a feasible route toward high-performance carbon nanotube-based thermoelectric composites.