Both silicon and carbon have been proposed to be important light elements in the Earth’s core, in particular in the inner core. Here we performed melting experiments on the Fe-Si-C ternary system at ~50, ~136, and ~200 GPa and determined the liquidus phase relations and the solid/liquid partition coefficients (D) of C and Si. The liquidus field of Fe shrinks at higher pressures, which narrows down the possible outer core liquid composition. Our data also demonstrate that the Fe-Si binary eutectic liquid reduces its Si concentration to ~8 wt% with increasing pressure to 330 GPa. We found that the inner core is not Fe-Si-C-S alloy but likely includes hydrogen when considering the low DC and the strong enhancement of DSi with increasing liquid C abundance. The present-day core does not include as much as ~6 wt% Si, suggesting that at least a part of “missing” Si could be sequestrated elsewhere.