The invention discloses a preparation method of mPEG2000-DSPE sodium salt, which comprises the following steps of: reacting a compound I with a compound II so as to obtain a compound III; reacting a compound VII with ethanolamine so as to obtain a compound IV; and then reacting the compound III with the compound IV so as to obtain a compound V; removing benzyl protecting groups in the compound V by using palladium on activated carbon and ammonium carbonate so as to obtain a compound VI; and finally, reacting the compound VI with alkali. The method is less in process steps, an operation of preparing the compound V by using the compound I can be completed through a one-pot reaction, so that the technological operation is simple, and an effect of industrial production is easily achieved; and a situation of taking DSPE as an intermediate is avoided, thereby reducing the production of impurities and improving the overall yield; and the reaction selectivity is high, the occurrence of side reactions and by-products is reduced, and the risk and cost of reaction are lowered.