The invention relates to a novel melamine water reducer which comprises the following raw materials by mass: 18.7-23.2% of melamine, 38-42.6% of formaldehyde, 20-27% of sodium bisulfite, 2-3% of sulfuric acid, 3-5% of liquid alkali, and 20-30% of water. The method of the invention comprises the following steps: adding water, melamine, the formaldehyde solution into a reaction vessel, stirring and heating to 50-60 DEG C for reaction for 1-3 hours, performing heat preservation and reaction at 60-75 DEG C for 1-5 hours, adjusting the pH of the solution to 8.5-9.5 by the liquid alkali solution; adding sodium bisulfite, heating, reacting at 84-90 DEG C for 1-3 hours, maintaining the pH at 10-11; finally cooling the solution to 50 DEG C, adjusting the pH value to 5-6.5 by 30% sulfuric acid, continuing the reaction for 1-2 hours, neutralizing the solution to obtain a pH of 7, discharging to obtain the finished product. The water reducer prepared by the invention has strong water retention capacity for concrete, a high water-reducing rate, high early strength of concrete, low air entraining, and less slump loss.