Method for preparing rare-earth carbonate

This invention relates to a prepn. method for rare-earth metallic compound and uses aqueous solution of sulfuric acid-rare earth as raw liquid and ammonium bicarbonate as precipitating agent to proceed precipetating, ageing, filtering and scrubbing; while adding ammonium bicarbonate under stirring, solid rare earth carbonate as seed crystal is added; or after adding ammonium bicarbonate under stirring, solid rare earth carbonate as seed crystal is adding under stirring. It has simple process, high-purity product, large grains, high recovery of rare earth oxide, and low cost.