The tangential restitution coefficient (Rt) is a critical parameter in predicting the movement process of rockfall impacts. Its accuracy directly determines the precision of rockfall trajectory predictions and consequently affects the effectiveness of preventive structures installed.Traditionally, due to a lack of deep understanding of the rockfall impact motion mechanism, Rt has been considered closely associated with slope characteristics. However,the influence of rockfall and kinematic characteristics has received less attention.Although some preliminary explorations have been made, no consensus has been achieved on the influence of certain controlling factors. This paper leverages theories of impact dynamics and findings from previous research to identify significant control factors related to Rt, encompassing both kinematic and rockfall characteristics. Based on this, systematic studies were conducted using a specially developed multifunctional rockfall impact test apparatus to analyze the influence of these control factors on Rt.The findings reveal several key relationships: At low incident velocities (V), a positive correlation exists between V and Rt. However, at high V, this impact becomes less significant, and a negative correlation is observed on slopes of loose medium.For vertical impacts on inclined planes, Rt generally decreases with increasing impact angle, while for oblique impacts on horizontal surfaces, Rt increases with a larger impact angle. Rt is insensitive to changes in rotational speed, though a comprehensive understanding of this relationship requires considering both impact posture and specimen shape.On both dense rock and loose medium slopes, block size shows contrasting relationships with Rt. Larger Rt values were typically obtained in the impact tests of blocks with higher geometrical asymmetry, with angular blocks having generally higher Rt values than non- angular ones. Under conditions of lower or higher impact energies, Rt showed an increasing or decreasing trend, respectively, with the increasing block hardness.These discoveries not only provide critical references for precise rockfall trajectory prediction and the design and deployment of effective preventive measures but also widen the perspective for more comprehensive and in- depth research on the impact- motion process of rockfalls in subsequent studies.