The invention provides modified polyether polyhydric alcohol and an application thereof in polyurethane foam materials. The preparation method of the modified polyether polyhydric alcohol comprises the following steps of: a compound A is reacted with polyether polyhydric alcohol, the compound A is an anhydride and/or dicarboxylic acid compound containing a polymerizable double bond, which preferably selected from one or two of maleic anhydride and itaconic anhydride, maleic anhydride is preferable; 2) the product obtained in step 1) is reacted with an epoxy compound containing a polymerizabledouble bond in the presence of a catalyst to obtain the modified polyether polyhydric alcohol. The obtained modified polyether polyhydric alcohol has more active sites, the polymerizable double bond is used for end capping, the modified polyether polyhydric alcohol is used as a dispersion stabilizer to be applied to the synthesis of the copolymer polyhydric alcohol, and the modified polyether polyhydric alcohol has the advantages of better dispersion stability, filterability and low viscosity.