The invention relates to environmental-friendly water paint. The water paint comprises the following substances: 40-50 parts of a hyperbranched polyurethane emulsion, 30-40 parts of an acrylic ester emulsion, 5-15 parts of water, 1-15 parts of nanometer titanium dioxide, 0.1-3 parts of a thickening agent, 2-4 parts of a film forming additive, 0.1-0.6 part of an antifoaming agent, 0.01-0.3 part of a disinfecting preservative, and 0.1-4 parts of a dispersing agent. The invention also relates to a preparation method for the water paint. An active group in the water paint is an alpha amino. The invention begins with a film forming substance of a paint film, firstly, the alpha amino is prepared into histidine of which the alpha amino is protected, then the histidine is introduced into film forming resin, and the tail end of the hyperbranched structure of a resin molecule is just the active group alpha amino, so that the active group alpha amino is furthest exposed, effective active groups in the resin molecule are greatly improved, and the effective active groups are in wide contact with methanal; therefore, methanal is converted into a steady nontoxic chemical compound, and the purpose of effectively removing methanal is achieved.