Electroreduction of water into hydrogen holds promise to deal with growing environmental pollution and energy crisis, but it relies on efficient catalysts for both hydrogen/oxygen evolution reaction, that normally contain precious metal. Here, based on first principles calculations, we identify Co-anchored α-InSe as a bifunctional catalyst that can operate for both hydrogen/oxygen evolution reaction. The chemical activity can be largely enhanced or optimized by electrostatic potential due to the polarization, even better than traditional one containing precious metal. Both hydrogen/oxygen evolution reaction are dependent on polarization direction of α-InSe and could occur on different polarization domains separately of α-InSe, that providing a way for future design of bifunctional catalysts without precious metals based on two-dimensional ferroelectric substrate.