The invention discloses a glass-wool inorganic heat-insulating coating. The coating comprises the following components in percentage by mass: 20-35% of glass-wool, 15-25% of styrene-acrylic emulsion or silicone acrylic emulsion, 30-59% of water, 3-4% of a film-forming aid, 1-2% of an antifreezing agent, 1-2% of a defoaming agent, and 1-2% of a dispersant. A preparation method of the coating comprises the following steps: putting glass-wool into a ball mill, and ball-milling the glass-wool for 15 minutes at a rotating speed of 20 revolutions per minute; taking out the glass-wool subjected to ball-milling, and putting the glass-wool into a mixing agitator; sequentially adding styrene-acrylic emulsion or silicone acrylic emulsion, water, the film-forming aid, the antifreezing agent and the dispersant according to the proportions above, carrying out low-speed agitating for 1 hour at a normal temperature of 10-40 DEG C, and then carrying out high-speed agitating for 3-5 hours; adding the defoaming agent, and carrying out low-speed agitating for 3-5 hours; and finally, tinning the obtained product, so that a coating finished product is obtained. The coating is simple in preparation method and good in waterproofness, flame resistance and heat-insulating property; and the raw material is abandoned old glass, so that the problem of environmental pollution is solved, and the cost of the coating is reduced.