A floor coating agent with excellent adhesion and hardness, and a construction method using the same are proposed. The floor coating agent includes a primer layer applied onto a surface of floor and then cured, and a floor coating layer applied onto the primer layer and then cured, wherein the primer layer is produced from a mixture of a self-emulsified epoxy resin, an acrylic polyol resin, a defoaming agent, 1,3,5-triglycidyl isocyanurate, dodecanedioic acid, anhydrous sodium citrate and water, and the floor coating layer is produced from a floor coating layer composition including an acidic copolymer alkyl ammonium salt, zinc oxide, oxalic acid, ammonium hydroxide and distilled water. Based on this configuration, floor coating agent can improve durability, abrasion resistance, gloss and the like of a floor surface, based on excellent adhesion to the floor surface and superior surface hardness.