Ab initio calculations show that the coupling between antiferrodistortive(AFD) distortions and magnetization in perovskite Bi2FeMnO6 is prohibited to make magnetization rotate as on-site Coulomb interaction($U$) is larger than 2.7 eV, where anomalies in antiferromagnetic(AFM) vectors and band gap varying with on-site Coulomb interaction can be observed. This coupling is attributed to the antisymmetric Dzyaloshinskii-Moriya interaction(DMI) driven by the eg-eg states AFM interaction and charge redistribution with respect to different AFD distortions.