Special attention in the role of convection in vapor crystal growth has been paid since some single crystals under microgravity environments less than 1 $g_0$ exhibits a diffusive-convection mode and much uniformity in front of the crystal regions than a normal gravity acceleration of 1 $g_0$. The total molar fluxes show asymmetrical patterns in interfacial distribution, which indicates the occurrence of either one single or more than one convective cell. As the gravitational level decreases form 1 $g_0$ down to $1.0{ imes}10^{-4};g_0$, the intensity of convection, indicative of the maximum molar fluxes, is reduced significantly for ${Delta}T=30K$ and 90 K. The total molar fluxes decay first order exponentially with the partial pressure of component B, PB (Torr) for 20 Torr ${leq}PB{leq}$ 300 Torr, and two gravity accelerations of $g_y=1;g_0$ and 0.1 $g_0$.