It was found via high temperature crystal growth in situ observation device that the morphology of KABO crystal varies with the degree of supersaturation of the crystal growth solution. The existence of ［BP3］3- and ［AlO4］5- growth units was proved by the results of high temperature Raman measurement of KABO crystal growth solution. The mechanism of KABO crystal morphology evolution was analyzed through the growth-units model of anionic coordination-polyhedra. It was found that the morphology of KABO crystal was determined simultaneously by its inner structure and the growth units. The kinds and dimensions of KABO growth units vary in solutions with different supersaturation, so accordingly, the morphology of KABO crystal changes from hexagonal to triangular morphology, and then from triangular to hexagonal dendritic morphology.