The invention provides a hyperbranched 
polymer and a preparation method thereof, wherein the preparation method comprises the steps of taking 
methyl acrylate, 
ethanolamine, 2-bromoethanol and propandioic acid as raw materials to synthesize a hyperbranched poly (amine-ester) nuclear molecule comprising a 
bromine terminal group; taking cuprous 
bromide and 2,2-bipyridyl as a catalyst and a coordinating agent; respectively 
grafting acrylic acid and single methyl 
oxygen radical sealed allyl 
polyethylene glycol into the hyperbranched poly (amine-ester) comprising 
bromine terminal group by means of an 
atom transfer radical polymerization method so as to obtain a hyperbranched 
polymer. The invention further provides a hyperbranched type water 
reducing agent of polycarboxylic acid series mainly comprising the hyperbranched 
polymer and the application thereof, wherein the water 
reducing agent improves the faults of existing water 
reducing agent of which the adding quantity is large and the 
cement adaptability is bad and the like,. and has the advantages that the adding quantity is low, the water reducing efficiency is high, the loss of 
slump is less, the compatibility to the 
cement is good, the frozen resistance is strong and the like, the properties of the product are stable, and the water reducing agent has no tendency of layering and precipitating and has no 
toxicity and 
pollution after storing for a long time.