This present work evaluates the local structure and electrochemical behavior of the LiCl-KCl-SmCl₃ melt to facilitate the efficient reprocessing of spent nuclear fuel (SNF). At 723 K, the radial distribution function, coordination number, and structure factors were adopted to understand the local structure of LiCl-KCl and LiCl-KCl-SmCl₃ based on first-principles molecular dynamics (FPMD) simulation. We found the SmCl₃ slight effect on LiCl-KCl melts in short-range order and its influence on the distribution of Li-Li intermediate-range order. Moreover, the diffusion coefficient of Sm(III) 2.012×10^-5 cm²/s in LiCl-KCl melts was determined by analyzing the mean square displacement. The electrochemical behavior of Sm(III) was conducted in the temperature range from 673 K to 823 K by a series of electrochemical methods. According to the theory of Matsuda and Ayabe, the Sm(III) + e^- = Sm(II) is a quasi-reversible process. The diffusion coefficient of Sm(III) was measured by the chronoamperometry method, which verified the credibility of the FPMD simulation. Furthermore, this work explored the exchange current density of Sm(III)/Sm(II), whose value is between 0.826×10^-3 and 2.383×10^-3 A·cm^-2, by the linear polarization.