The invention relates to a light burning-avoiding heat-insulating material and a preparation method thereof, and belongs to the field of heat-insulating materials for construction. The raw materials used in the method comprise the following compositions in mass percent: 40-50% of low-grade kieselguhr, 35-45% of a binding agent A, 5-10% of coal ash, 5-10% of a binding agent B, and 0.2-0.5% of a foaming agent. The manufacturing technology comprises the steps of raw material pre-treatment, material blending, molding and maintenance. According to the invention, the heat preservation material prepared by adopting the method has the characteristics of light weight, high strength, small heat conductivity coefficient, heat preservation, thermal insulation, excellent sound-proof performance, high temperature resistance, aging resistance, acid and alkali resistance, zero radioactivity, environmental protection, energy conservation and the like.