Crystalline boron nanowires (BNWs) have been grown on the entire surface of diamond powders by a solid–solid reaction approach. A series of analysis technique were employed to investigate the as-grown BNWs. The as-grown BNWs are in length of several micron-meters with the diameter ranging from 20–200nm. And the BNWs crystalline structure is identified to be tetragonal structure. Systematic analyses reveal that the growth models such as classic VLS (vapor–liquid–solid) model are not applicable to explain this kind of BNW's growth mechanism. Hereby, an extended VLS model is proposed which can perfectly interpret the BNW′s growth process on diamond surface and match experiment results very well.