Piezoelectric energy harvesters are expected to power trillions of miniaturized sensors. We theoretically analyze nanogenerators with aligned piezoelectric nanorods using formulaic solutions and finite-element simulation using COMSOL Multiphysics in order to explore the possibility of achieving excellent output performance. It is shown that for the same piezoelectric materials, using a rod-shaped unit will increase the piezoelectric constant d33 by 33% compared with using a film, owing to less substrate clamping. In addition, when normal force is applied, the stress is concentrated in the nanorods. Therefore, in the case of applying normal force, the aligned nanorod array can generate an output power one or more orders of magnitude higher than films within the same volume. This type of nanogenerator will play an important role in the integration with miniaturized sensors in the off-resonant mode.