Laser power converters (LPCs) used in wireless energy transmission can realize noncontact power supply under extreme conditions and provide continuous energy support to unmanned probes, which is believed to play an essential role in the exploration of deep ocean. However, commercially available LPCs usually employ III–V semiconductors as light absorbers due to their industrial maturity. In order to match the underwater 450∼540 nm laser source, it requires an epitaxial growth method to tune the bandgap of those materials, which is highly costly that severely restricts the industrial preparation of LPCs on a large scale. Herein, the potential of perovskite in the application of underwater LPCs is presented theoretically by constructing MAPbBr3 LPC and its theoretical power conversion efficiency (PCE) of 48.55% is demonstrated. Moreover, a microcavity (MC) constructing strategy to further improve the device performance is proposed, in which the transfer matrix method and an admittance‐based antireflection condition approach are combined for the optical simulation. By modulating the MC condition, the significant optical resonance inside the device while avoiding the obvious light reflection is realized. As a result, MC LPCs can obtain a simulated PCE of 64.27%, which is highly competitive with the existing UV–vis LPCs.