The invention provides aqueous degradable environment-friendly ink for printing, a special decoloring agent and a preparation method of the ink. The degradable environment-friendly ink contains dye, wherein the dye is azo-dye or triphenylmethane dye, or macromolecular dye synthesized by one of azo-dye or triphenylmethane dye, and aqueous macromolecular material. The preparation method of the degradable environment-friendly ink comprises the steps of dispersing, grinding and filtering aqueous acrylic resin, dye, de-ionized water, an antifoaming agent, a flatting agent, surfactant and amine materials in a high-speed disperser and a sand mill in sequence. The special decoloring agent is sodium dithionite or 2Na2CO3.3H2O2. The ink has the advantages of environment friendliness, no harmfulness, good safety, stable performance and good printing effect. When waste papers is recycled, the ink can be decoloured quickly under the action of the matching decoloring agent, and therefore, the problems that organic solvent in the oily ink volatilizes, the waste paper is difficult to deink and sewage pollution is serious are solved.