The invention discloses a high-adaptation and fast-dispersion phosphonic acid-based water reducing agent and a preparation method and application thereof. The molecular structure of a high-adaptationand fast-dispersing phosphonic acid-based polymer is in a comb shape, and a molecular main chain contains a rigid benzene ring, and is formed by condensation polymerization of a phenoxy compound. A polyoxyalkenyl structure is a steric hindrance side chain, adsorption functional groups are phosphate radical and carboxylate radical, and the phosphate radical and carboxylate radical are distributed irregularly. The high-adaptation and fast-dispersion phosphonic acid-based polymer can improve the adaptation to low grade aggregates and low activity industrial waste residues, improves the flowing property of concrete with a low water-binder ratio, and improves the mechanical and enduring properties of the concrete.