Knowledge of thermodynamics of multimetallic nanoparticles is of great importance in prediction and advancing the understanding of synthesis, characterization, and applications of metal nanoparticles. In this work, molecular dynamics simulations were performed to investigate the melting characteristics and behaviors of a ternary Fe-Ni-Cr nanoparticle (19.17 wt.% Cr, 11.72 wt.% Ni, and the rest Fe). It was found that the melting of the nanoparticles starts from the surface and proceeds gradually inwards to the core, indicating a liquid nucleation and growth melting mode. During heating, severe Cr segregation with increasing temperature were observed, and the nano Cr clusters prefer to aggregate mostly at the surface due to lower surface energy and stronger cohesive interactions of Cr atoms than Fe and Ni. Moreover, the melting temperature of the nanoparticles decreases as the particle radius decreases, and there exists a linear relationship between the melting point and the inverse of the radius. This signifies the feasibility of the linear depression effect for the size-dependent melting of Fe-Ni-Cr nanoparticles accompanying surface segregation and aggregation. The findings in this work are believed to provide the atomic scale understanding of mechanisms of melting and surface segregation of ternary Fe-Ni-Cr nanoparticles.