The invention discloses a method for synthesizing a platinum atom cluster based on complexation thermal reduction. The method comprises the step: carrying out complexation and thermal reduction reaction through diglycol, dihydroxyethyl amine and platinum ions, thus preparing the platinum atom cluster. According to the method disclosed by the invention, the defects in the prior art that the particle size is difficult to control, particle distribution is non-uniform, and a platinum nano-material is difficult to well form the platinum atom cluster are overcome, and the platinum atom cluster in large specific surface area, uniform particle diameter and good catalytic performance is prepared; the platinum atom cluster prepared by the invention has very good catalytic performance, and high activity and high stability of a single platinum atom and the platinum atom cluster are improved; the method for synthesizing the platinum atom cluster is simple and easy, a new method is provided for designing of the next generation of catalysts, and huge potential of reducing the high cost of a commercial platinum catalyst is obtained.