One of the major challenges in seawater reverse osmosis (RO) desalination plants is the feed water quality which causing a significant RO membrane fouling. Natural organic matter (NOM) is mainly consisting of humic substances (HSs) which derived from natural degradation of some organic substances within the ecological systems and from human activities and vastly meet fouling species in natural water resources. The significant reduction (63.4%) of total organic compounds (TOC) on surface of calcite ooid grains after 3 hrs. has been studied. According to the molecular dynamic simulations (MDS), the interaction between different main molecular building blocks forming HSs and CaCO3 crystal of fabricated calcite ooids surfaces was accomplished to interpret the action of its adsorption modes.