The invention discloses a preparation method of isomeric alcohol polyoxyethylene polyoxypropylene ether. The method is characterized by comprising the following step that in the presence of a certainamount of a rare-earth complex catalyst, an isomer alcohol is taken as a starting agent and is polymerized with ethylene oxide and epoxypropane for preparing the isomeric alcohol polyoxyethylene polyoxypropylene ether. According to the invention, the rare-earth complex catalyst is added, so that the degree of unsaturation of the prepared isomeric alcohol polyoxyethylene polyoxypropylene ether is low, and thus a good technical effect is achieved.