<p>Flexible energy storage and harvesting devices, as core components of the flexible electronic system, have driven the transformation of electronic system from “external power supply” to “self-powering” and from “fixed forms” to “adaptive configurations”, thus playing an important role in the advancement of wearable technology, the internet of things, and other related fields. MXenes, a class of two-dimensional transition metal carbides, nitrides, and carbonitrides, emerge as promising candidates for flexible energy storage and harvesting devices, attributed to their excellent conductivity, mechanical flexibility, and tunable interfacial characteristics. Specifically, the interfacial characteristics of MXenes, including surface energy, surface terminations, and interlayer spacing, have a decisive influence on the performance of MXene-based energy devices. This review summarizes the influence of microcosmic interfacial characteristics on macroscopic properties, the interfacial regulation strategies, and applications in flexible energy storage and harvesting of MXenes, concluding with current challenges and perspectives to guide the design of high-performance MXene-based energy devices.</p>