Chrysotile asbestos tailing was broken down into active magnesium oxide and silicon dioxide by roasting. The activation product of Chrysotile as raw materials was used to prepare acicular basic magnesium carbonate by the carbon–ammonia method. The effect of the carbonization temperature, aging temperature, aging time, and the mole ratio of NH3•H2O and Mg2+ were studied on the form and percent conversion of the acicular basic magnesium carbonate. The structure, thermal properties and crystal morphology of the sample were analyzed by XRD analysis, thermal analysis and optical microscope, respectively. The results show that acicular basic magnesium carbonate prepared at the best conditions: carbonization temperature is at 50°C, aging temperature is at 70°C, aging time is for 4-5 hours, and the molar ratio of NH3•H2O and Mg2+ is 2:1. In this condition, the formation rate of specula basic magnesium carbonate is more than 82%. Its chemical formula which is 4MgCO3•Mg(OH)2•4H2O is obtained by XRD and thermal analysis, and the aspect ratio of the sample of the acicular basic magnesium carbonate was about 30 which was tested by optical microscope.