This study improves the microscopic understanding of electrostatic potential to a reservoir’s wettability, defined as the tendency of oil-wet or water-wet. Current conclusions about the wettability of oil reservoirs continue to be elusive, relying on some outdated or one-sided physical and chemical knowledge which requires further investigation. Poorly addressed problems on wettability alteration in a reservoir might lead to severe surfactant adsorption and finally reduce the efficiency of Chemical Enhanced Oil Recovery (EOR). By measuring the zeta potential in our Brine-Oil-Minerals (BOM) model system, the effects coming from acid/ basic characteristic of crude oil and operation conditions, such as temperature, salinity and ion composition, are comprehensively evaluated. Combined with the future contact angle measurement, this work aims to demonstrate the influence of electrostatic potential for fluid-fluid and rock-fluid on the wetting state of BOM model system. The micro-mechanisms learned by this study are expected to improve reservoir characterization, reservoir modeling and simulation, thereby optimizing reservoir management, well technology, production methods, and facilities.