Transient global simulations were carried out to study the effects of the furnace pressure on oxygen (O) and carbon (C) coupled transport in an industrial directional solidification (DS) furnace for silicon ingots. The global simulations of impurity transport, taking into account the O and C impurity segregation, chemical reaction on the graphite surface, evaporation of SiO and dissolution of CO at the melt-gas surface, were based on a fully coupled calculation of the thermal and flow fields of the DS furnace . It was found that the furnace pressure affects the intensity and structure of argon flow above the melt surface, which further influences the O and C impurities transport in the DS furnace . The O concentration in the grown ingot decreases with the decreasing furnace pressure. While the C concentration first decreases, and then increases when the pressure is smaller than 200 mbar due to the strong diffusion effect of the CO through the gap between crucible and cover. The numerical predictions of O and C concentrations agree well with the experimental measurements.