The soft magnetic properties of Fe-Ta-N films are decided by grain size and lattice deformation. In high Ta content films, the grain size is smaller than 10nm, so the coercivity is decided by lattice deformation, which is increasing with the content of interstitial N atoms. The dependence of coercivity on sputtering power and total pressure can be explained well by the change of lattice deformation. The optimum soft magnetic properties migrate to high partial nitrogen pressure at high sputtering power, or to low partial nitrogen at high total pressure.