To face energy crisis and environmental pollution, clean renewable energy sources provide the most promising way for energy and environmental sustainability. Piezoelectric energy harvesters can be practically assembled using low-cost solution assembly methods to convert ambient mechanical energy, such as waves, wind, and others, into electricity. In this study, we demonstrate the assembly of fully functional piezoelectric energy harvester fabricated by vertically grown hydrothermal ZnO nanorods/nanosheets on aluminum foil as a composite. The advantages of this device are the process simplification of plating electrodes and the high-temperature heat treatment with aluminum foil substrate. Both factors are beneficial to improve the power output and efficiency of piezoelectric energy harvesters with ZnO thin films. Firstly, the zinc oxide seed layer is fabricated on the aluminum foil by sol-gel dip-coating method at different annealing temperatures. Subsequently, ZnO nanocrystals arrays are grown by hydrothermal method on ZnO seed layers. From the results, it shows that while the seed layer is annealed with atmosphere furnace at 400°C and then grown with hydrothermal method, mixed nanorods and nanosheets in the morphology of ZnO thin film are obtained and presented with the best piezoelectric property. By measuring the output voltage and output power of this device, it shows that with the vibration amplitude of 0.5cm and the frequency of 10Hz, the output voltage and output power can be reached at 3.70V and 268mW, respectively. More details of the influence of processing parameters on the nanostructures and piezoelectric properties of ZnO-based energy harvester are demonstrated in this study.