Based on the characteristics of magnesium oxides which are very abundant in the chrysotile asbestos tailing and mineralogical research on asbestos tailings, the authors employed the ammonium sulfate calcination method to extract magnesium from asbestos tailing, and used the leaching liquid as the raw material to prepare the basic magnesium carbonate. The influence of the reaction temperature on the phase, morphology and structure of the product during the preparation of the basic magnesium carbonate were characterized by means of XRD, SEM, FT-IR and TG-DTA. The results indicated that the products were needle-like magnesium carbonate hydrate at the temperatures below 65℃, flake-like magnesium carbonate hydrate at the temperatures higher than 85℃,and short column-like or granule-like magnesium carbonate hydrate and flake-like magnesium carbonate hydrate at 75℃. Heated magnesium carbonate hydrate would remove part of H₂O and CO₂, which turned into flake-like basic magnesium over 100℃. Research performed in this paper has some theoretical and practical significance for environmental protection and comprehensive utilization of chrysotile asbestos tailings.