A ferroelectric crystal with charge-free surface conditions contains polarized domains which can form a flux closure with zero net polarization. In the presence of an external electric field, the flux closure in a two-dimensional continuum reorients its spontaneous polarization to align with the field. Based on this concept of ferroelectric switching coupled with mechanical straining, we demonstrate the working principle of a ferroelectric nano-actuator. The behavior of the actuator is explored under the action of electro-mechanical loading and its mechanism is simulated with a 2D phase-field model. The design of nano-actuator is modified to achieve greater actuation displacements by bending a thin device.