Fe80Ni20 thin films with different thickness values are prepared by the molecular beam vapor deposition technique, respectively, in the cases with applying no magnetic field and with applying a 6 T magnetic field perpendicular to the surface of substrates. Film property studies show that as film thickness value increases, the coercive force in-plane decreases, which is in accordance with Neel theory, and that the squareness ratio first quickly increases, and then slowly decreases. The 6 T magnetic field restrains coalescence and abnormal growth of grains, and reduces surface roughness. Therefore, with 6 T magnetic field applied during the film preparation, the coercive force of thin film is less and the squareness ratio is larger than that with no magnetic field applied. The thin films are anisotropic in-plane with applying no magnetic field, but isotropic with applying a 6 T magnetic field.