A numerical simulation has been performed to investigate the effect of a cusp magnetic field on the melt flow, thermal field and oxygen concentration during the Czochralski silicon crystal growth process. The results show a decrease in the oxygen concentration due to the reduction in size of the secondary flow cell that formed between the Taylor-Proudman vortex and the buoyancy-driven one. There is a significant reduction in the size of the secondary now cell when the magnetic field is applied. As a consequence of the higher strength of the magnetic field there is a significant decrease in the oxygen concentration along the melt-crystal surface. The oxygen concentration is also very sensitive to the crucible rotation rare. There is an optimum crucible rotation rate for obtaining the lowest oxygen concentration. The oxygen concentration is lower for higher argon flow rare. The oxygen concentration decreases as the zero-Gauss plane (ZGP) moves from the free surface towards crucible bottom. When the ZGP is far from the free surface, the secondary flow cell appears and then the oxygen concentration increases. There is an optimum position of the ZGP to obtain [he lowest the oxygen concentration. (C) 2013 Elsevier B.V. All rights reserved.