We investigate the possibility of growing a uniform binary compound crystal in space numerically, employing a new crystal growth technique called the Graded Solute Concentration method. We develop a numerical calculation method of the growth of binary crystals. The calculation method is applied to the crystal growth of an InAs-GaAs binary semiconductor by the Bridgman and zone methods and the effect of buoyancy convection induced under microgravity conditions on the crystal growth process is investigated. We find that the concentration field is disturbed and, as a result, the solution-crystal interface is deformed by buoyancy convection in the case of the Bridgman method even when the gravitational acceleration is as low as 10(-6)g, which is supposed to be the gravity level in the International Space Station. We also find that buoyancy convection is reduced in the case of the zone method and therefore uniform binary crystals may be grown by the zone method.