Numerical analysis is conducted to clarify the formation mechanisms of silicide nanoparticles synthesized in an induction thermal plasma maintained at atmospheric pressure. The induction thermal plasma is analyzed by an electromagnetic fluid dynamics approach, in addition to a multi-component co-condensation model, proposed for the silicide nanoparticle synthesis. In the Cr-Si and Co-Si systems, silicon vapor is consumed by homogeneous nucleation and heterogeneous condensation processes; subsequently, metal vapor condenses heterogeneously onto liquid silicon particles. The Mo-Si system shows the opposite tendency. In the Ti-Si system, vapors of silicon and titanium condense simultaneously on the silicon nuclei. Each system produces nanoparticle diameters of around 10 nm, and the required disilicides, with the stoichiometric composition, are obtained. Only the Ti-Si system has a narrow range of silicon content. The numerical analysis results agree with the experimental findings. Finally, the correlation chart, predicting the saturation vapor pressure ratios and the resulting silicon contents, is presented for estimation of nanoparticle compositions produced in the co-condensation processes.