Motivated by the strong magnetic anisotropy of the Ising antiferromagnet alpha-CoV2O6, we measure the magnetization curve by designating magnetic field deviating ∼ 30 and 60 degrees from the c axis within the bc plane. At 4.2 K, both pulsed and DC fields magnetization curves including an additional spin flip is observed with increasing magnetic field, revealing that there exist two fractional magnetization plateaus irrelevant to the type value of 1/3 in alpha-CoV2O6. We found that the fractional magnetization plateaus are in unstable state because of the incompatibility between the increasing and falling fields. The irreversible magnetization process can be explained as a behavior of metastable state.