Recently, it has been proven that the biaxial strain (ε), electric field (E) and interlayer distance (d) can effectively modulate the electronic structure and magnetic properties of two-dimensional (2D) van der Waals (vdW) heterostructures, which have potential applications in spintronic devices. Here, the electronic structure and magnetic properties of 2D g-C₃N₄/Li-adsorbed Cr₂Ge₂Te₆ vdW heterostructures are investigated using first-principles calculations. Their lattice structures are seriously affected by adsorption combination. With external stimulation, the band gap of the heterostructures changes. The heterostructures are metallic at ε = −6% and −4%, and others are n-type semiconductors, where the band gap is 23 meV at ε = 6%. In addition, the magnetic moments of g-C₃N₄ in the adsorption systems are in the range from 0.029 to 0.226 μ_B. The vdW heterostructures show in-plane magnetic anisotropy (IMA) at ε = −6%, −2% and 6% and perpendicular magnetic anisotropy (PMA) at ε = −4%, 0, 2% and 4%. On applying an electric field and changing the interlayer distance, the vdW heterostructures show PMA. These results are significant to the low-dimensional spintronic devices.