The invention discloses a phosphorizing agent for improving the surface brightness of an electro-galvanized steel plate. The phosphorizing agent is characterized by consisting of the following substances in percentage by weight: 13.0 to 15.0 percent of phosphoric acid, 8.0 to 12.0 percent of nitric acid, 4.0 to 8.0 percent of zinc oxide, 2.0 to 5.0 percent of starch phosphate, 0.6 to 0.8 percent of magnesium nitrate, 0.4 to 0.8 percent of zinc nitrate, 0.5 to 1.0 percent of nickel nitrate and the balance of water. According to the phosphorizing agent, the brightness of a phosphate film is improved to be more than 75, so that the surface quality of the phosphorized electro-galvanized steel plate is improved.