The invention provides a method for preparing 2-hydroxyethylhydrazine. The method comprises the following steps: taking chloroethanol, acetone azine and water to react at certain temperature, so as to prepare 2-hydroxyethylhydrazine hydrochloride; neutralizing by utilizing sodium hydroxide to obtain the 2-hydroxyethylhydrazine. In a reaction process, excessive acetone azine and water in a reaction process so that the chloroethanol in a reaction system reacts completely; after reaction is finished, the water and the residual acetone azine are removed by decompression distillation; then decompression rectification is carried out to obtain a 2-hydroxyethylhydrazine finished product. Compared with the prior art, hydrazine hydrate with an expensive price and ethylene oxide with relatively large dangers are not used; a process is simple to operate, the equipment investment is less, the energy consumption is low and side effects are few; in the reaction process, recycled byproduct acetone is a raw material for synthesizing the acetone azine and can be circularly utilized, so that the production cost is low.