This paper discusses the correlation between soft magnetic properties and microscopic magnetic structure in Co-(0–6 at%) Fe-(7–10 at%) Ta-N nanocrystalline films. Increasing the Fe content improves the soft magnetic properties of the films by decreasing the local anisotropy fluctuation. The temperature dependence of the coercive force indicates that the decrease in the magnetocrystalline anisotropy at room temperature due to the increase in Fe content plays an important role in decreasing the local anisotropy fluctuation. Furthermore, with increasing Fe content the film magnetostriction decreases, which suggests that the magnitude of the linear magnetostriction decreases. On the other hand, the uniaxial magnetic anisotropy energy Ku is reversibly induced by magnetic annealing in all films. As the Fe content is increased from 0 to 6 at% the magnitude of Ku gradually rises, and the Ku of films containing 6 at% Fe is about twice as large as that of films not containing Fe.