In the context of low-viscosity aqueous lubrication, this study systematically investigates the lubrication mechanisms of polyacrylic acid (PAA) solutions. It combines experimental techniques with molecular dynamics simulations to elucidate the effects of concentration-dependent molecular structures and temperature-dependent adsorption stability. Results show that with increasing PAA concentration, the friction coefficient first decreases and then increases, with optimal lubrication observed at 0.2%. Higher concentrations lead to increased PAA adsorption, elevated acidity, and molecular aggregation, resulting in surface corrosion and intensified wear. At high temperatures, while adsorption energy remains stable, enhanced chain flexibility and entanglement raise viscosity, reduce film fluidity, and accelerate wear. These findings provide valuable insights for optimizing water-based lubrication systems using PAA additives.