[Objective] The variation characteristics of concentrated water flow resistance influenced by different angles between bedrocks and ground surface on the hillslope were explored to provide scientific basis for the construction of soil erosion model in the karst trough valley area.[Methods] To investigate the changes of Manning roughness coefficient (n) of concentrated flow and its influencing factors on the karst trough valley hillslope with different angles between bedrocks and ground surface, the laboratory scouring simulation experiments were conducted under the conditions of three slope gradients (10°, 15° and 20°), three inflow rates (5, 7.5, 10 L/min) and six angles between bedrocks and ground surface (30°, 60°, 90°, 120°, 150° and 180°) . [Results] ① The Manning coefficient n of concentrated flow increased rapidly and then increased slowly or tended to be stable with the scouring time. The average value of n was ranked as: 180° > 150° > 90° > 30° > 120° > 60°. ② When the angle between rock and slope surface was greater than 30 °, the relationship between n and water depth (h) was significant, and when the angle was 30 °, the relationship between n and Reynolds number (Re) was not significant, and there was a significant negative power function correlation between n and Froude number (Fr). ③ The ratio of Manning roughness coefficient to flow depth (n/h) increased at first and then decreased with the increase of angles between bedrocks and ground surface. ④ The n/h presented negative power correlation with Re when the angle between bedrocks and ground surface was greater than 30 °, and n/h showed no significant relationship with Re when the angle between bedrocks and ground surface was 30°. The relationship between n/h and Fr was always not significant. [Conclusion] Manning coefficient n was strongly affected by the angles between bedrocks and ground surface, and decreased first and then increased with the increase of angles between bedrocks and ground surface on the karst trough valley hillslope.