Abstract: In ascertain the evolution process and generating mechanism of roll waves, the variation rules of hydraulic parameters of roll waves under five kinds of roughness, five different energy slopes and eight unit discharges was studied by using a fixed bed test and ultrasonic measurement technology. The results showed that at the fixed section, the wave velocity increased as a power function with increasing unit discharges, while the relative wave velocity exhibited an opposite trend. The wave height and relative wave height first increased and then decreased as unit discharges increased. With the increase of roughness, wave velocity decreased while relative wave velocity increased. However, the wave height and relative wave height both decreased with an increasing roughness. The influence of energy slope on roll waves was also related to roughness. Under a small roughness, the wave velocity increased as a power function with the increasing energy slope while the decreasing power function between relative wave velocity and energy slope was found. Wave height first increased and then decreased while the relative wave height increased continuously. However, under a large roughness, the relative wave velocity increased and the wave height remained stable during the whole process with an increasing energy slope. In contrast, although the relative wave height increased first but this trend became less obvious and the height even decreased as energy slopes increased. Therefore, taking into account the influence of average hydraulic parameters were taken into account when adopting the relative wave velocity and relative wave height, which could better reflect how various factors affected the evolution process of roll waves.