This study presents a numerical framework to model the effect of surface tension on a flexoelectric energy harvesting system with liquid inclusions. The equivalent Young’s modulus and Poisson’s ratio of the liquid inclusions embedded in flexoelectric composites considering the surface tension are derived for the first time. An extended isogeometric analysis (XIGA) based on non-uniform rational B-splines (NURBS) is developed to model and solve the electromechanical response of weak discontinuities in flexoelectric composites. The interface between liquid and solid materials is implicitly represented by the level set method. Several numerical examples are presented as linear dielectric solids embedded with liquid inclusions under mechanical compression and different electric circuit configurations, including square matrixes and truncated pyramids. The simulation results indicate that a significant enhancement in the electromechanical coupling coefficient can be obtained by considering the effect of surface tension in open- and closed-circuit configurations. The maximum electric potential and energy conversion are higher in the open-circuit configuration. In addition, the XIGA simulation shows that the energy conversion of the flexoelectric devices increases as the size of the structural system and Young’s modulus of the flexoelectric material decrease. The maximum energy conversion capability of the flexoelectric composite, including the effect of surface tension, is enhanced by 32.4% with a central inclusion and 57% or higher with random inclusions. Finally, the influence of the length scale on the flexoelectricity is analyzed.