The present invention relates to a method of preparing a super absorbent polymer (SAP), and more specifically to a method of preparing a SAP including the steps of spraying the monomer composition on a substrate having a hydrophobic surface of a certain tan angle and carrying out a UV polymerization on a polymerization reactor having a slightly hydrophilic surface. The present invention can improve the conversion rate of polymerization because the shape of the monomer solution is changed from prior sheet form to droplet form so that UV rays reach the deeper layer of the droplets, can minimize or simplify the recycling process because it is easy to control the particles of the prepared polymer, and can provides the SAP of high caliber by narrowing the particle diameter distribution and improving the uniformity.