This article describes the preparation of nitrogen‐phosphorus‐doped boron nitride (BN@APP) as a multifunctional nanofiller for flame‐retardant and thermal conductivity in polybutylene succinate (PBS). The BN@APP was obtained by a one‐step ball milling method. The improvement of thermal conductivity effectively reduces the generation of toxic smoke during PBS combustion. After incorporating 1.0 wt% BN@APP into the PBS, the thermal conductivity of the PBS composite is increased by 62.8%. The heat and toxic smoke are reduced significantly, the heat release rate, total heat release, and total smoke rate of PBS composites were dramatically reduced by 28.2%, 23.5%, and 44.8%, respectively, compared to pure PBS. This research offers a prospective route to prepare highly flame‐retardant composites that have low‐toxicity and smoke.