Gold is widely used in electronic products and decorative products. Its stable chemical properties can not only play an important role in the protection of the substrate, golden color also has a decorative function. Although electroplating gold and immersion gold can deposit gold coatings, the qualities of the gold coatings remain some problems. The basic premise of electroplating successfully is that the workpiece is connected with the power source. In addition, the quality of the gold coating by electroplating is also greatly affected by the shape of the workpiece, so that the circuit board with complex lines is difficult to deposit great quality coating efficiently through electroplating. Immersion gold is through the corrosion of the substrate to achieve gold deposition. Once the corrosion is excessive, the “black pad” phenomenon will happen, which is adverse to the corrosion resistance of the coating. In recent years, with the rapid development of electronic products, higher requirements have been put forward for the quality of circuit boards. The gold layer plays a very important role in ensuring the reliability of electronic devices. Chemical reduction gold plating is an important research field to overcome the above defects, especially the eco-friendly cyanide-free gold plating that has become a research hotspot. This paper summarizes the research and basic principles of common reducing agents including sulfite, dimethylamine borane, hypophosphite, hydrazine, ascorbic acid, sodium borohydride, thiourea, and other reducing agents as well as promoters in cyanide and cyanide-free gold plating solutions, especially the catalytic activity of nickel and gold on these reducing agents. Most reductants are catalyzed by only one of these two metals, so the combination of two or more reductants is a feasible scheme to keep the reaction rate high in both the initial stage and the later stage of deposition. The deposition of thick gold depends on reductants which can oxidize rapidly with the catalysis of gold. Also, the future development in cyanide-free reduction gold plating has been prospected.