Preparation method of methyl-glycine diacetate tri-sodium

The invention relates to a preparation method of methyl-glycine diacetate tri-sodium, successively comprising the following steps of: preparation of hydroxy acetonitrile solution, preparation of iminodiacetonitrile solution, preparation of methyl-flycine nitrile diacetonitrile crystal, preparation of methyl-glycine diacetate tri-sodium (MGDA-3Na) and preparation of solid product MGDA-3Na. In the method, the yield of methyl-flycine nitrile diacetonitrile crystal is higher than 92%, the total yield of MGDA-3Na can reach more than 86%, the content of NTA (nitrilotriacetic acid) is less than 0.08%; and the equipment investment and energy consumption in the hydrocyanic acid refining process are saved on the premise that high yield and low toxic side product content are met, and the hydrocyanic acid refining process is not required, so that the production cost is reduced and the environment pollution is reduced.