In this Letter, a method is proposed to increase the power output of piezoelectric energy harvesting via gradient auxetic structures. This method is validated through a gradient auxetic piezoelectric energy harvester, which combines a cantilever beam and a gradient auxetic structure. Compared with the normal uniform auxetic structure, the gradient auxetic structure can contribute to a more uniform strain distribution of the piezoelectric cantilever beam; thus, the proposed gradient auxetic energy harvester can produce higher power than the uniform auxetic energy harvester without increasing the stress concentration at the same time. Finite element simulation is performed to analyze the characteristics of the gradient auxetic energy harvester. From the experimental results, under the base excitation of 1 m/s², the power density of the gradient auxetic energy harvester is increased by 356% and 55%, respectively, compared with the conventional plain energy harvester without auxetic structure and the uniform auxetic energy harvester.