Based on a space experiment of lysozyme crystallization, a two-dimensional model was designed to study numerically the post-nucleation transport in the liquid/liquid diffusion crystallization of proteins. The initial concentration distributions for protein and salt were calculated with a purely diffusive process before nucleation. The results of simulation show that a noticeable depletion zone of protein also exists around a growing crystal in liquid/liquid diffusion chamber under 0g condition. The gravity-driven convection decreases the thickness of the depletion zone seriously. Furthermore, influenced by the solutal convection, the protein concentration and solution supersaturation at the crystal/solution interface are much higher in 1g case than in 0g case. In addition, in our case the computed gravity-driven convection had more complicated pattern and higher strength than those known for the batch and vapor diffusion crystallizations. Our simulation also shows that the uniformity of concentration and supersaturation distributions at the crystal/solution interface could be improved by the gravity-driven convection. The lower uniformity in 0g case is owing to the initial gradient distribution of protein concentration in liquid/liquid diffusion crystallization, but it could be improved by adjusting the initial conditions of protein crystallization.