Water contains a great amount of potential energy, out of this, an energy harvesting and converting solution from water is very promising for green renewable energy. In this paper, a hybrid energy harvester (HEH) is proposed, which has a combination of piezoelectric and electromagnetic mechanisms for energy conversion. Two piezoelectric energy harvesters (PEH) and two electromagnetic energy harvesters (EMH) can work synchronously to achieve high-performance output. The structural variables of the prototype are studied and analyzed through the self-designed experimental test system. When the prototype is assembled with optimal structural parameters, the maximum output voltages of a single PEH and EMH are 56.24 V and 1.016 V. The maximum output power of HEH is 22.78mW, which is 21 % higher than that of PEH and 253011 % higher than that of EMH. Subsequent underwater tests and a series of application tests were performed to verify the performance of the HEH, showing that it can easily power some commercially available sensors and small electronic devices. Experimental results show that HEH is promising in wireless self-powering and self-sensing. It provides a new power supply scheme for laying power supply without grid for monitoring equipment in deep sea and ocean environment.