The invention discloses one method of producing polyether polymer dispersant and polyether polymer, wherein the dispersant is a copolymer macromolecule prepared by the propylene oxide or ethylene oxide with an average molecular weight of 6000 to 20000, with containing at least one benzene ring group and one polymerizable carbon-carbon double or triple bond polymer. The preparation method of the dispersant is: synthesizing a basic polyether polyol, adding a cyclic dicarboxylic anhydride into the polyether polyol, then the polyether polyol is reacted with an epoxy compound with the polymerizable double bond, and capping with an epoxy compound to obtain the dispersant; preparing the polymer polyol by the basic polyol, an unsaturated vinyl monomer styrene and acrylonitrile, a polymerization initiator, the dispersant and an optional chain transfer agent; the basic polyether is a polyether polyol with a functionality of 3 to 8.