Amphiphilic polymer micelles have been extensively explored to encapsulate hydrophobic drugs for cancer drug delivery.The mostly used approaches to fabricate drug-loaded micelles are the dialysis method and precipitation method,in which water is added to the polymer/drug solution in a watermiscible solvent such as THF,DMSO or DMF.It is generally assumed that with adding water,the drug would precipitate in the hydrophobic part forming the drug-loaded core-shell structure.However,it is puzzling that as-fabricated micelles always suffer a serious burst release problem and some drugs such as paclitaxel (PTX) and 7-ethyl-10-hydroxycamptothecin (SN-38) are difficult to be loaded.There is no theoretical and elaborate understanding on this problem.