Non-covalent interactions, particularly van der Waals (vdW) interactions, are crucial in chemistry, physics, and life sciences. Accurate calculation of both the repulsive and attractive parts of vdW potentials is essential for a reliable description of dissociation curves in vdW systems. The diffuse quantum Monte Carlo (DMC) method is known to be able to calculate vdW interactions accurately at equilibrium distances. However, its performance on vdW interaction energies at non-equilibrium distances has not been investigated. In this work, dissociation curves for ten vdW interacting systems with dispersion interactions, dipole-induced dipole interactions and dipole-dipole interactions are calculated using the DMC and some low-level methods,