The presence of thin aqueous films and their stability have a profound effect on the interactions between oil/brine/rock interfaces. In a previous report, we proposed that hydration forces, originating from the overlap of hydrated layers of different surfaces in the presence of sodium chloride, played an important role at short range. In the present work, divalent ions were introduced to the liquid films and, the mechanisms in improving oil recovery from low-salinity brine and the low-salinity effect at the molecular level were revealed. Through a direct force-measuring technique of chemical force microscopy (CFM), the functionalized atomic force microscopy (AFM) tips felt a solid surface to mimic the oil/rock interactions in brine. It was found that not only did the van der Waals and electrostatic forces have a great effect on this process due to the interactions between the charged interfaces of oil/water and water/solid, but also some important additional interactions appeared at short range under a variety of salinity concentrations or compositions. Taking into account the important role of structural forces under a small distance, the force profiles were fitted well with the theory of extended Derjaguin-Landau-Verwey-Overbeek (denoted by EDLVO) through a double-exponential or Gaussian model. Interestingly, low adhesion appeared in the presence of sodium sulfate, because hydration forces contributed to the resultant force depending on the intrinsic properties of the solvent or solute molecules, while in the presence of calcium chloride, high adhesion emerged due to the dispersion interaction between water and hydrocarbon molecules, as well as the reorientation or restructuring of water molecules with tiny breakage of hydrogen bonds. Therefore, on the basis of the EDLVO theory, additional forces were suggested to play an important part in short range, proposing a better understanding of the effect of divalent ions on the thin liquid films in the process of increasing oil recovery.