The work aims to determine the decisive factor for influencing the alloy electrodeposition process and find out the concentration of sodium citrate corresponding to maximum electrode reaction rate by investigating the effect of sodium citrate on the electrodeposition behavior of Zn-Ni-Mn alloy. The electrodeposition behavior of Zn-Ni-Mn alloy in bath with different sodium citrate concentration was studied by cyclic voltammetry curve (CV), rotating disk electrode (RDE), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The surface morphology and elemental composition of alloy were characterized by scanning electron microscopy (SEM) and energy spectrum analysis (EDS). The electrodeposition of Zn-Ni-Mn was an irreversible process according to the CV analysis. When concentration of sodium citrate was 0.6 mol/L, co-deposition potential peak was most positive (-1.642 V, vs. Ag/Ag+). It was demonstrated by RDE analysis that electrodeposition of Zn-Ni-Mn alloy was a process controlled by dynamics and diffusion and with sodium citrate concentration increased; the influence of mass transfer on alloy deposition became weakened. The EIS analysis indicated that the rate of electrode reaction was determined by relaxation caused by intermediate adsorbate and diffusion of ions. When sodium citrate concentration was 0.6 mol/L, an inductance arc appeared at low frequency, making the polarization resistance (Rp) decrease and reach to the minimum (349.68 Ω?cm2). From CA curves, alloy nucleation rate decreased and the nucleation mechanism changed from instantaneous nucleation to continuous nucleation gradually with sodium citrate concentration increased. SEM and EDS results showed that the grain of Zn-Ni-Mn alloy became coarser with increasing of sodium citrate concentration. Grain developed from the cellular to the polygonal shape with decreasing of Mn content in alloy. The variation regularity of Zn content in the alloy was consistent with the electrode reaction rate. The electrodeposition process of Zn-Ni-Mn is determined by dominant species of Zn2+ in electrolyte. When sodium citrate concentration is 0.6 mol/L, Zn2+ ions mainly exists as [ZnHCit]- complexes in electrolyte. The intermediate product, [ZnHCit2-]ads, can be adsorbed on the surface of cathode, that decreases concentration polarization greatly and obtains the fastest electrode reaction rate.