Niobium (Nb) is widely used in aerospace, nuclear energy and superconducting fields, due to its excellent comprehensive physical and chemical properties. In the preparation methods of the Nb coating, the molten salt electrodeposition technology has fast deposition rate, high cathode current efficiency and is suitable for complex shape components, which is expected to realize large-scale industrialized production and application. Since the current widely used fluoride-supported electrolyte system is highly toxic and environmentally unfavorable, there is an urgent need to carry out the development of a more environmentally friendly all chloride supporting electrolyte system. To achieve the regulation of the molten salt’s physical properties of the supporting electrolyte and the stabilization of the complexing ions, this study adds CsCl to the NaCl-KCl system to prepare an all chloride supporting electrolyte system and investigates the effect of CsCl on the molten salt’s physical properties of the supporting electrolyte and the electrodeposition behavior of the Nb coating. The results showed that the eutectic temperature of the NaCl-KCl-CsCl ternary mixed molten salt was about 485 °C. With the increase of CsCl content, the initial crystallization temperature of molten salt decreased at first and then increased, the density increased, and the conductivity and surface tension decreased. CsCl affected the mass transfer rate of ions in molten salt by changing the initial crystal temperature and conductivity of molten salt, and then affected the surface quality of electrodeposited Nb coating, and its preferred content was about 60 wt.%. The addition of CsCl can make the reduction potential of the oxygen-containing complex ion NbOF63- in the molten salt negative to that of NbF72-, which was helpful to obtain Nb coatings without oxygen impurities.