This study was focused on the slope along the New Central Cross-Island Highway in Yushan National Park. By surveying the destructed sites, geological and geographical data, and using an axonometric chart to perform a statistical analysis of various internal characteristics, the development mechanism of rockfall in the study area and the effect of various internal factors on rockfall were discussed. The survey revealed that the destruction of the sloped in the study area was mainly due to rockfall. Other forms of destruction were due to debris slide, slump, circular failure, or a combination of the above. Based on their number and relative influence, the primary internal development mechanisms of rockfalls are (in order of importance): rock mass of discontinuity caused by tectonic movement, decompression joints caused by road construction, erosion caused by embedded sandy shale, and ruptures caused by explosives used during road construction. Analysis of various internal factors and results from statistics showed that internal factors made a larger contribution to rockfall in the study area. These factors included: the presence of structure lines (mesoscope fold axis, fault line), the spatial relationship between discontinuity orientation and slope, the number of discontinuity sets, and slope angle. The internal factors that made a relatively larger contribution to the destructive scale of rockfall included: the distance between and density (Jv value) of discontinuity, slope height, and slope length.