Thermal chemical vapor deposition (TCVD) produces relatively pure boron nitride nanotubes (BNNTs), while it may not be enough for production. A ball milling.annealing process is beneficial in quantity; however, the generation of the impurity is most concerned. In this regard, we explored the dual syntheses of BNNTs based on the chemical reactions of solid and gaseous boron with nitrogen, respectively. Synthesis mechanisms for both were also analyzed by presenting the stepwise reaction routes. With these understandings, the production of BNNTs could be increased, while the impurities are reduced when compared with the individual one, once the experimental conditions are optimized.