A macromonomeric stabilizer, a preparation method thereof, a method for preparing a polymeric polyol using same, and the polymeric polyol prepared. Also disclosed are a soft polyurethane foam obtained by foaming a composition of the polymeric polyol prepared and a polyisocyanate, and a molded product comprising the soft polyurethane foam. The preparation method of the macromonomeric stabilizer comprises the following steps: reacting a polyol with a tricarboxylate not comprising a polymerizable ethylenically unsaturated double bond, or a derivative thereof, to form an adduct; and reacting the resulting adduct with an epoxide comprising a polymerizable ethylenically unsaturated double bond. The macromonomeric stabilizer of the present invention has a low viscosity, comprises a plurality of active sites, and can be directly used in subsequent reactions. The preparation method of the macromonomeric stabilizer can be carried out under normal pressure, without the need for end-blocking with ethylene oxide.