<p>This study focuses on the friction plate of the composite oil groove in a hydro-viscous clutch. It considers the effect of oil film temperature and pressure on the hydro-viscous drive characteristics during the transmission of the friction pair and establishes a numerical calculation model for different flow rates entering the friction plates under rated slip conditions. Based on the research of the rectangular groove morphology, deficiencies in oil film pressure and temperature uniformity were found. Two improved radial oil groove structures, trapezoidal and arc-shaped, were proposed based on the calculation results. Through simulation studies of these two new types of oil grooves, it was found that, without altering the circumferential groove structure, the arc-shaped radial oil grooves significantly improve the pressure and temperature distribution of the oil film. When the oil film inlet flow rate is 1 L/min, the pressure difference of the oil film near the arc-shaped radial oil grooves is reduced from 14,408&#xa0;Pa to 9493&#xa0;Pa, and the temperature rise range of the oil film is decreased from 0.22&#xa0;K to 0.14&#xa0;K. Additionally, the torque transmitted by the oil film is increased by 2.90%. The results indicate that the composite grooved friction plates with arc-shaped radial oil grooves offer better optimization, providing new theoretical references for the future design of hydro-viscous clutch.</p> Graphical Abstract <p></p>