The energy harvesting was investigated on relaxor ferroelectric terpolymer P(VDF-TrFE-CFE) utilizing nonlinear capacitance variations. We introduce the thermodynamic cycle — Ericsson cycle and Stirling cycle into the energy harvesting process, which could evidently improve the harvested energy. The theoretical model of thermodynamic cycles was established and analyzed. The uncontrollable voltage would lead to the sample broken. Accordingly, Ericsson cycle was chosen for energy harvesting. Based on it, we measured the characterization of P(VDF-TrFE-CFE) terpolymer, especially discussed the tunability of permittivity by applying electric field. The harvested energy was simulated versus different temperature range and different maximum electric field, the maximum harvested energy based on Ericsson cycle could be achieved at around 210 mJ/cm3 between 20° C to −20° C.