The invention provides a new process for preparing medium molecular weight hydroxyethyl starch materials. In the ultrafiltration step of the production process flow, a filter membrane with the molecular mass cut-off of 300,000 and a filter membrane with the molecular mass cut-off of 100,000 are used in turn for ultrafiltration, and an ultrafiltration process of only using a filter membrane with the molecular mass cut-off of 100,000 is replaced, so that the content of endotoxin in the hydroxyethyl starch is effectively reduced, the molecular weight of the hydroxyethyl starch is more concentrated in a medium molecular weight range, the safety and quality of the product are improved, and the produced medium molecular weight hydroxyethyl starch (including hydroxyethyl starch 130/0.4 and hydroxyethyl starch 200/0.5) materials and preparations meet the standard of state pharmacopoeia.