NOVELTY - A nano-grade lithium carbonate preparing method involves heating water and mixing with lithium hydroxide monohydrate. Water-soluble dispersing agent is added to the mixture and stirred. Carboxamide is mixed with water. The source of lithium carbonate is successively added to a water heat source synthesis reaction kettle followed by stirring tank closure and a hydrothermal synthesis reactor. The reactor is placed in an oven, heated and quenched and filtered. The lithium carbonate lithium carbonate slurry cake is washed with hot water. The lithium wet material is heated and dried.    USE - Method for preparing nano-grade lithium carbonate.    ADVANTAGE - The method enables preparing nano-grade lithium carbonate with high purity.    DETAILED DESCRIPTION - A nano-grade lithium carbonate preparing method involves heating water to 60-80 degrees C and mixing with lithium hydroxide monohydrate with a mass ratio of 2:1. Water-soluble dispersing agent is added to the mixture, and stirred for 10-20 minutes to obtain a lithium source mixture, where the mass ratio of water soluble dispersants and the lithium source is 0.1-1%. Carboxamide is mixed with pure water with mass ratio of 1:1 to obtain carbonate source, where the molar ratio of the carboxamide and lithium hydroxide monohydrate is 1:1.80-1.95. The source of lithium carbonate is successively added to water heat source synthesis reaction kettle, followed by sufficient stirring tank closure and hydrothermal synthesis reactor. The reactor is placed in an oven at a rate of 3 degrees C/minute, heated to 100-120 degrees C for 5-10 hours and quenched with cooling water after opening the autoclave and filtered. The lithium carbonate lithium carbonate slurry cake is washed with 2 to 4 times boiling hot water to obtain lithium carbonate wet material. The hydrothermal synthesis reaction vessel is lined with polytetrafluoroethylene ethylene stainless steel products. The lithium wet material is heated at 250-350 degrees C and pressure of -0.1 to -0. 08 Mpa, dried for 8-15 hours to obtain nano grade lithium carbonate powder.