A piezoelectric energy harvester with a non-uniform cantilever structure is presented for highperformance energy harvester. The optimal layout length of the piezoelectric layer, the effect of the key design parameters on this optimal length and its underlying mechanism have been systematically investigated by the theoretical prediction, the finite element analysis and the experimental verification. As a result, the optimal PZT layout length for the maximum power is approximately 1/5 total length of the cantilever with a large proof mass, which results from the large average strain distribution in the functional layer. The width of cantilever, the thickness of PZT layer and the modulus of substrate have an apparent effect on the optimal PZT layout length, whilst the thickness of proof mass, the total length of cantilever and the applied acceleration indicate a minimal effect. Based on this optimization strategy, a non-uniform cantilever piezoelectric harvester with the optimal piezoelectric layer length performs high power density (30 mW/cm(3)) and good stability (3.3 million cycles) at the low resonant frequency of 46 Hz. This significant improvement bears great guiding significance on the design and practical application of such strain-induced cantilever energy harvesters. (C) 2018 Published by Elsevier Ltd.