In the steep mountainous areas in northwest Xinjiang, where rock mass is broken seriously due to intense freeze thaw weathering, rockfall is one of the most common geological hazards on highway high slopes. Engineering geological investigations on geological hazards along a segment of the G219 highway was conducted, indicating that rockfalls on the high slopes threaten the safety of vehicles on the highway seriously. In this study, a combination of field investigations, laboratory experiments and numerical simulation methods was performed to identify unstable high slopes, simulate the rockfall trajectories and assess the rockfall hazard in the study area. The results show that there are five high slopes (i.e., W01, W02, …, W05) where rockfall hazard is extremely serious. Considering both the total kinetic energy and the accumulation rate of blocks, rockfall influence area zonation was performed, leading to the conclusions that the sections of highway on W01 to W05 are located at the medium-intensity low-accumulation zone, high-intensity medium-accumulation zone, high-intensity low-accumulation zone, high-intensity low-accumulation zone and medium-intensity high-accumulation zone, respectively. Based on the analysis, a zonation map was accomplished, which could help engineers select effective mitigation measures against rockfalls to avoid casualty and property losses.