Abstract: Effect of magnetic field on thermocapillary convection in a double-diffusive liquid layer was investigated by numerical simulation, in which both the thermal Marangoni effect and solutal Marangoni effect were considered. The computational results show that thermocapillary convection is effectively weakened by external magnetic field and the convective pattern is changed. With magnetic field intensity increasing, the convective intensity is decreased gradually; the diffusive effect in the process of heat and mass transfer is strengthened, and the solute concentration distribution indicates a gradient along the horizontal direction. Therefore, the pure diffusion process in crystal growth can be realized as magnetic field intensity is sufficiently large.