The invention discloses a preparation method of low-free-alcohol fatty alcohol-polyoxyethylene ether. The preparation method includes the steps of firstly, using fatty alcohol R-OH as the initiator to have reaction with ethylene carbonate under the effect of a basic catalyst to obtain ethoxyl alkyl ether; secondly, after the ethoxyl alkyl ether is heated, adding ethylene oxide in the presence of the basic catalyst to perform addition reaction, and adding acetic acid for neutralizing after the reaction to obtain the low-free-alcohol fatty alcohol-polyoxyethylene ether. The preparation method has the advantages that the two-step synthesizing technology is used, the synthesized fatty alcohol-polyoxyethylene ether is low in free alcohol content, few in byproducts, high in effective component content, and the like; compared with similar products prepared by the existing technology, the free alcohol content of the fatty alcohol-polyoxyethylene ether is lowered from 6% to 0.7%, and the quality of the fatty alcohol-polyoxyethylene ether is increased greatly.