This paper presents the theoretical modeling and multiplescale analysis of a novel nonlinear piezoelectric energyharvester composed of a steel beam, piezoelectric films and acompressive spring at the moveable end. The harvesterexperiences mono- and bi-stable regimes as the potential energyfunction varies from a flatted parabolic shape with a single wellto a double-well shape along with the increasing spring predeformation. Using the energy method and Galerkinapproximation, the governing equations are derived with twohigh-order coupling terms induced by the axial motion of thebeam. The analytical strategies and implementation processes ofthe method of multiple scales are systematically introduced toanalyze the nonlinear dynamics of the harvester either in themono- or bi-stable status. Numerical simulations are performedto verify the approximate analytical solutions of frequencyresponses and phase portraits. The influence of the electricalresistance, excitation level and the spring pre-deformation on thevoltage outputs and dynamics of the harvester are investigated.Results show that the spring pre-deformation has a slightinfluence on the performance of the mono-stable system, but anevident effect on that of the bi-stable system.