Vibration is a ubiquitous phenomenon in nature.Piezoelectric materials can convert the mechanical energy of external vibrations into electrical energy, providing energy for micro-electromechanical systems, wireless sensor networks, embedded systems, etc., thereby reducing the device’s dependence on battery power. To broaden the working bandwidth of the piezoelectric-energy harvester and improve its energy-harvesting efficiency, this study designs a tilted asymmetric composite piezoelectric-energy harvester, and obtains the natural frequency and modal shapes of each group of the harvester through theoretical analysis. Through finite-element analysis, the correctness of the theoretical derivation is proved, and the influence law of the number of piezoelectric cantilever beams on the piezoelectric-energy harvester in this design is verified. The results show that the tilted asymmetric composite piezoelectric-energy harvester can harvest vibration energy under multiple modes and improve the energy-harvesting efficiency.