Based on a phenomenological model, the electrocaloric effects accompanied with the ferroelectric to paraelectric phase transition in relaxor ferroelectric 0.9PbMg1/3Nb2/3O3–0.1PbTiO3 thin film were investigated. The model reproduces the essential features of the experimentally observed behavior and also gives a description of the electric field dependence of the electrocaloric effect. The simulated results reveal many intriguing features of electrocaloric effect including electrocaloric entropy changes, heat capacity changes and temperature changes as functions of temperature due to different electric fields shifts ΔE. A relative cooling power and refrigerant capacity due to applied electric field shift were calculated.