Dielectric elastomer (DE) can undergo large deformation when subjected to external forces or voltage, leading to the variation of the capacitance. A novel DE sensor is proposed to detect compressive force. This sensor consists of a series of elements made of DE membrane with out-of-plane deformation. Each element experiences highly inhomogeneous large deformation to obtain high sensitivity. Both experimental and theoretical studies are conducted to optimize the performance of the sensor element, and the effects of the prestretches and the aspect ratios on the sensitivity are achieved. Results from the theoretical analysis based on continuum mechanics agree well with the experimental data. Furthermore, the reliability of the sensor element is illustrated by additional experimental investigation on the operation after 2000 cyclic loadings. This study provides guidance for the design and performance analysis of soft sensors.