Abstract: Same initial and final temperature comparative method and isothermal method were chosen to synthesize hydromagnesite particles under microwave irritation and water bath heating.SEM,XRD,and CSD were used to characterize crystal structure,surface morphology,and particle size distribution of the samples at different stages.Chemical titration analysis was used to track the change of magnesium ion concentration in crystallization process.Experimental results showed that hydromagnesite crystals were constructed of lots of self-assembled nano-sheets.Microwave accelerated the crystallization of magnesium carbonate,that is to say microwave could accelerate the assembly of primary nano-particles in magnesium carbonate crystallization,thus enhanced the growth rate of hydromagnesite and then increased the crystal size,but did not change the crystal habit;transition paths of hydromagnesite at different temperatures were different，the amorphous substance assembled into hydromagnesite at higher temperature and nesquehonite intermediate would appear at lower temperature,and the micro-morphology and assemble manner of hydromagnesite nano-sheets by different phase-transfer processes were not the same. 

Key words: hydromagnesite, reactive crystallization, microwave