The invention relates to a preparation method of lightweight aggregate and an inorganic heat insulation material which takes the product thereof as a main heat insulation source. The lightweight aggregate is prepared by two surface treatments after the sudden cooling after the high-temperature melting by pitchstone and the introduction of gasification materials, the water absorption is low and the adhesion is good. The inorganic heat insulation material takes the obtained lightweight aggregate with the excellent performances as the main heat insulation sources and takes cement as an adhesive material, lightweight powder, expansion agent, acrylic short fiber, re-dispersible emulsion powder, cellulose and calcium formate are further added to adjust the mechanical and the construction performances of the heat insulation material. The prepared inorganic heat insulation material has excellent heat insulation, fire resistance, durability, long service life, environmental protection, energy conservation, material economy and better social and economic values.