This paper is to further discuss the second-order spin-wave instability processes for the ferrite sample of ellipsoidal shape using Schl?mann and Patton methods. The theoretical expressions of the second-order spin-wave instability threshold for film samples are different from Anderson-Suhl formula. The threshold calculations for single crystal YIG films under three different perpendicular pumping configurations show that the calculated thresholds are reasonably consistent with the experimental results for three configurations, and the threshold values given theoretically and experimentally are in close relationship with the oreintation of the linearly polarized microwave magnetic field.