The invention discloses a four-arm star-shaped block polycarboxylic acid super-plasticizer and a preparation method and application thereof. A molecule with four hydroxyls is first terminated with a halogenated carboxylic acid derivative, then a halogen-containing terminated four-arm molecule is used as a structural core and a non-traditional unsaturated carboxylic acid derivative is used as an arm to prepare a polymer, and finally the star-shaped four-arm block super-plasticizer is synthesized after acid hydrolysis and separation and purification. The conventional unsaturated carboxylic acidis not used for polymerization, the controllability of the structure can be improved, and the irritation of the unsaturated carboxylic acid in production is reduced. A synthesized water-reducing agenthas excellent molecular structure controllability. The product is solid, has low blending amount, high dispersibility and high fluidity, and has the characteristics of convenient transportation and storage, low water absorption and low corrosivity.