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The polymer/hexagonal boron nitride (h-BN) thermal conductive composite an excellent candidate for thermal management materials due to its insulation properties. However, it is a challenge to achieve efficient large-scale exfoliation of h-BN through melt blending to balance thermal conductivity and mechanical properties. In this work, an innovative melt mixing strategy using the co-rotating non-twin screw extruder (NTSE) was developed to prepare the high-density polyethylene (HDPE)/h-BN composites with excellent overall performance. The results were well compared with those of conventional twin screw extruder (TSE). The NTSE triggers chaotic mixing and provides a strong elongation flow field capable of h -BN efficiently exfoliating into a few layers, while simultaneously ensuring uniform dispersion and distribution within HDPE. The in-plane thermal conductivity and elongation at break of the NTSE composite with 10 wt% h-BN addition were 7.63 W∙m−1 K−1 and 653.1 %, which were 74.7 % and 70.3 % higher than those prepared by TSE, while the enhancement rates rose to 174.6 % and 74.4 % when 30 wt% h-BN was added, respectively. The in-plane thermal conductivity enhancement ratio of NTSE was more than 3000 % when the h-BN content was higher than 10 wt%. Besides, the thermal stability, crystallinity, and thermal diffusion of the NTSE composites were also enhanced to different degrees. This strategy is efficient to coordinating the conflicting between the comprehensive performance and large-scale preparation of thermally conductive polymer composites. [Display omitted] • Efficient exfoliation of h-BN has been achieved by non-twin screw extruder. • Compared with twin screw, non-twin screw leads to higher orientation of BN. • The in-plane thermal conductivity increased 3076.3 % only with 10 wt% BN addition. • Non-twin screw can prepare polymer/BN with high comprehensive properties efficiently. [ABSTRACT FROM AUTHOR]