•The ZIF derivative is prepared via a facile pyrolysis approach.•The attenuation mechanism of the enhanced EMW absorption performance is revealed.•The polarization behavior is analyzed by simulating the electric field.•The composite nanotubes exhibit high-efficiency EMW absorption performance. Developing materials with a rational design of constituent and microstructure for excellent electromagnetic wave (EMW) absorption performance has been a puzzle for researchers. Herein, a type of zeolitic-imidazolate framework (ZIF-67) derivative embedded boron carbonitride (BCN) nanocomposites with a tubular microstructure are prepared via a simple, facile, scalable pyrolysis approach. The presence of BCN nanotube not only optimizes the impedance matching, but also promotes the dispersion of the Co nanoparticles, contributing to a high-efficiency utilization of conductive and magnetic losses of the ZIF derivative. Furthermore, the nanocomposites contain abundant heterogeneous interfaces, resulting in a high interfacial polarization capability, which is further confirmed by theoretical simulations. Consequently, BCN/C/Co composite nanotubes display superior EMW absorption properties. BCN/C/Co nanocomposites show a minimum reflection loss of − 56.7 dB at 12.4 GHz and an effective absorption bandwidth of 5.5 GHz at a thickness of 2.6 mm. This work thus provides a reliable reference for preparing lightweight, high-performance EMW absorbers.