The growth mechanism of core/shell heterostructured nanocrystals (h-NCs) is an important factor in uniform shell growth and hence determine the optoelectronic properties and photochemical stability. However, unlike conventional h-NCs synthesis system, III-V/II-V core/shell h-NCs has been relatively difficult compared to II-V/II-V core/shell h-NCs because of lattice mismatch and interface polarization. Herein, we have unveiled to control the growth mechanism of III-V/II-V core/shell h-NCs by tuning the facet-dependent growth. The controllable growth rate at each facet is responsible for diffusion-dependent growth that result in the shell morphology. Therefore, we provide critical insights into the growth method for III-V/II-V core/shell h-NCs by spectroscopic and calculation to make highly qualified nanocrystals.