The invention discloses a Pd/C catalyst and a preparation method thereof, the Pd/C catalyst takes carbon black as a carrier, and Pd metal nanoparticles are uniformly dispersed on the carbon black; themass percent of the Pd metal nanoparticles in the catalyst is 1%-70%, and the particle diameter is 2 nm to 8 nm. According to the Pd/C catalyst and the preparation method thereof, a liquid phase reduction method is used, ammonium hydroxide and NaOH are added to a Pd saline solution with certain concentration, a Pd complex ion solution is prepared, excessive reducing agent is added then, and the Pd complex ions are reduced on the dispersed carbon black carrier at certain reaction temperature. The Pd/C catalyst prepared with the method has excellent electrocatalytic activity in an oxygen-saturated 0.1 mol/L of HClO4 solution. The difficulties that the particle diameter of the Pd nanoparticles is large, clustering is difficult and the Pd/C catalyst is difficult to prepare in batches are solved.