The investigation of the dynamic response of lubricated surfaces remains a persistent research focus, owing to its dual importance in enhancing lubrication performance and enabling real-time condition monitoring. Currently, lubrication monitoring techniques primarily rely on indirect indicators such as temperature, spindle power, and oil analysis. While these methods demonstrate practical utility, they cannot provide direct real-time insights into microscopic interactions at friction interfaces. To examine this problem, this paper investigates the dynamic response characteristics of fluid-lubricated surfaces under hydrodynamic lubrication (HL) conditions. A theoretical model of acoustic emission (AE) signals specific to HL is developed, and a rheometer system is employed to experimentally analyze the correlation between lubricant flow characteristics and dynamic AE responses. The experimental results demonstrate that under HL conditions, lubricating greases and lubricating oils exhibit similar mid-to-low frequency spectra, with shear rate and viscosity identified as two key parameters influencing AE signal characteristics. These findings provide insights for real-time lubrication monitoring and optimization, showing potential significance for early fault detection in rotating machinery.