In this work, we successfully demonstrate that a crystal-structure regulation by simply altering the annealing temperature might be an effective way to enhance the electrocatalytic activity of perovskite oxides. We report a high-performance electrocatalyst with an orthorhombic double perovskite structure (i.e., PrBaCo2O5+delta, delta =similar to 0.52), which shows superior activity and durability towards hydrogen evolution reaction in comparison to a cubic perovskite oxide (i.e., Pr0.5 Ba0.5CoO3-delta) and a tetragonal one (i.e., PrBaCo2O5+delta, delta = similar to 0.76), despite the similar composition. The improvement of the electrocatalytic activity for hydrogen evolution reaction is mainly attributed to a high-degree structure distortion resulted from the high oxygen vacancy concentration, a large electrochemical active surface area, and a low charge transfer resistance. In addition, lattice oxygen species may provide an extra contribution to the enhancement of the hydrogen evolution reaction for Pr0.5Ba0.5CoO3-delta sintered at 1000 degrees C. Furthermore, a considerable correlation between O p-band centers and HER overpotentials is observed, and PBC-1100 with the highest O p-band center exhibits the best HER activity. These results indicate that the electrochemical performance of perovskite oxides could be effectively enhanced. Especially orthorhombic double perovskite oxides could be a new class of promising electrocatalysts.