The invention relates to a preparation method of high-purity dexrazoxane, which comprises the following steps of: (1) cyclization reaction: carrying out cyclization reaction between (S)-1, 2-propane diamine-N, N, N', N'-tetracetic acid or disodium salt of (S)-1, 2-propane diamine-N, N, N', N'-tetracetic acid and formamide, wherein a high boiling point solvent is used; (2) preparation of salt-containing crude product: evaporating the mixture, which is obtained after reaction, for removing the formamide by pressure reduction and concentration, adding organic solvent into the mixture, and filtering to obtain solid; (3) preparation of crude product: adding dioxane into the salt-containing crude product, heating for backflow, filtering, concentrating the filtrate, adding organic solvent into the filtrate to obtain the crude product of dexrazoxane; and (4) refining: adding the crude product of dexrazoxane into N, N'-dimethyl formamide, heating for dissolving, dropwise adding the solvent, carrying out crystallization, filtering to obtain solid, washing the obtained solid with the solvent, drying to finally obtain the high-purity dexrazoxane. The method for synthesizing dexrazoxane is stable in yield and easy in condition control; the product purity is higher than 99.5% and residual organic solvent is little, and the synthesis cost can be reduced.