Objective To solve trivalent chromium plating problems existing in chloride system and sulfate system. Methods Chromic formate was used as the main salt, and ammonium formate, urea and malic acid were used as the coordination agents. The effects of different factors, such as the concentration of Cr³⁺, ammonium formate, urea and malic acid, and pH value, temperature and plating time on the morphology, deposit rate and brightening range of trivalent chromium plated brass were studied by using Hull Cell and quadrate cell. Results The results showed that ammonium formate and urea could form active complexes with Cr³⁺respectively, and malic acid could buffer the pH value. The optimal condition was: 0. 4 mol / L Cr³⁺, 0. 5 mol / L ammonium formate,0. 2 mol / L urea concentration, 0. 05 mol / L malic acid, pH value of 3. 5 and temperature of 25 to 30 ℃ . Conclusion This technology of trivalent chromium electroplating in formate system had a wide bright range, and a plating can be gained with low porosity,bright and compact appearance, high deposit rate and excellent binding force with brass, the structure of the plating was mixed crystal. A decorative chromium deposit with a thickness of 1. 78 μm could be obtained after electroplating at the current density of 15 A / dm²for 5 min at room temperature.