The polycrystalline FeTaN thin films with the thickness range from 30 to 700 nm have been fabricated and their magnetic properties have been investigated. The results show that, with the increase of the thickness of the films, the polar plot of coercivity changes its shape, from the horizontal-ellipse-like, the circular to the vertical-ellipse-like, i.e. the in-plane easy axis undergoes a 90° switch. A model that considers the competition between magnetocrystalline anisotropy and magnetoelastic anisotropy induced by the stress as well as the distribution of the easy axis is proposed. Based on the model, the polar plots of coercivity are calculated and the results are well consistent with the experimental data. The torque experimental curves are also described well by the model.