The emergence of superconducting diode effect (SDE) provides a new platform to investigate the intertwining among band topology, superconductivity, and magnetism, thereby establishing the foundation for achieving ultra-low dissipation devices and circuits. The realization of the tunable zero-field SDE in two-dimension (2D) devices is significant for 2D circuits, however, there has been great challenges in the appropriate materials synergy and fine device design. Here, we report a zero-field SDE in the van der Waals (vdW) heterostructure constructed by the Ising superconducting NbSe₂ and ferromagnetic Fe₃GeTe₂ with a large perpendicular magnetic anisotropy. Based on the valley-Zeeman spin-orbit interaction (SOI) in NbSe₂, the magnitude and polarity of the zero-field SDE can be modulated by altering the ferromagnetic properties of Fe₃GeTe₂ through the application of pre-magnetized out-of-plane magnetic fields. Furthermore, the stable half-wave rectification of square-wave currents is achieved by utilizing the tunable zero-field SDE in the Josephson junction-free structure. The tunable zero-field SDE in 2D heterostructures brings new opportunities for understanding the coexistence of superconductivity and time-reversal symmetry breaking, and for fabricating 2D ultra-low dissipation circuits.