Existence of [B 3 -O 6 ] 3− hexagonal ring growth unit in melt solution of β-BaB 2 O 4 crystal was proved by the results of high temperature Raman measurements. A morphology evolution process of β-BaB 2 O 4 crystal was observed by a high temperature in-situ observation device. The crystal morphology varied with the supersaturation of growth melt solution. The mechanism of β-BaB 2 O 4 crystal morphology evolution was analyzed through the growth unit model. crystal morphology, Growth unit model: BBO crystal, Raman measurement