The invention relates to the technical field of building additives, specifically to a low-surface tension shrinkage reduction type polycarboxylate superplasticizer and a preparation method thereof. The preparation method comprises the following steps: putting a shrinkage reduction function macromonomer, a polyhydroxy polymer and water into a reaction kettle, controlling the temperature to 20-60 DEG C, respectively adding an initiator solution, a chain transfer agent solution and an unsaturated acid solution to obtain a reaction product, and adjusting the pH value of the obtained reaction product to 6.0-7.0 by using an alkali substance, thereby obtaining the low-surface tension shrinkage reduction type polycarboxylate superplasticizer. As a great amount of the shrinkage reduction function macromonomer is introduced into a polycarboxylic acid molecular structure through copolymerization, the polycarboxylic acid molecular structure has a shrinkage reduction function chain segment, a steric hindrance segment and an adsorption group segment, the problems that a straight chain shrinkage reduction agent is easily adsorbed by concrete and the shrinkage reduction performance is affected canbe solved by using a hyperbranched structure; in addition, the hyperbranched structure has large steric hindrance and has good dispersion performance when being used in concrete.