  Valleytronics has been widely investigated for providing new degrees of
freedom to future information coding and processing. Here, it is proposed that
valley polarization can be achieved by electric field induced magnetic
anisotropy (MA) transformation. Through the first-principle calculations, our
idea is illustrated by a concrete example of $\mathrm{VSi_2P_4}$ monolayer. The
increasing electric field can induce a transition of MA from in-plane to
out-of-plane by changing magnetic anisotropy energy (MAE) from negative to
positive value, which is mainly due to increasing magnetocrystalline anisotropy
(MCA) energy. The out-of-plane magnetization is in favour of spontaneous valley
polarization in $\mathrm{VSi_2P_4}$. Within considered electric field range,
$\mathrm{VSi_2P_4}$ is always ferromagnetic (FM) ground state. In a certain
range of electric field, the coexistence of semiconductor and out-of-plane
magnetization makes $\mathrm{VSi_2P_4}$ become a true ferrovalley (FV)
material. The anomalous valley Hall effect (AVHE) can be observed under
in-plane and out-of-plane electrical field in $\mathrm{VSi_2P_4}$. Our works
pave the way to design the ferrovalley material by electric field.
