The invention discloses a fly ash-based paper-making coating and a preparation method thereof and relates to the field of coatings. The fly ash-based paper-making coating comprises, by weight, 100-200parts of fly ash, 1-5 parts of a dispersing agent, 3-6 parts of a defoaming agent, 15-30 parts of an adhesive, 3-6 parts of a water-repellent agent, 1-5 parts of whitening agent and 1-3 parts of a bactericide. The method includes the steps of 1, placing deionized water in a dispersion container, adding the fly ash to the deionized water, and keeping high speed shear dispersion at the rate of 3100-4150rpm to add the dispersing agent to obtain a fly ash dispersion solution; 2), adding the defoaming agent, adhesive, whitening agent and bactericide in sequence at the time interval of 5-15 minutesto ensure the full dispersion and uniformity. The paper-making coating is prepared with bulk solid waste fly ash as pigment, which provides a new idea for comprehensive utilization of the fly ash, and the added value of the fly ash is improved.