Unstable rocks may often locate on steep slopes. Some stones separated by cracks are very large in volume and some stones are just boulders on steep slopes. Because the volume and unfavorable structure surface binding characteristics of a certain dangerous rock body can not be obtained easily by traditional measurement methods, prediction of the instability mode and dangerousness of dangerous rocks has been a challenge for the investigation of geological hazard to be caused by dangerous rock bodies. 3D laser scanning technology is a new technology developed in recent years. Because of the advantages of fast, accurate and non-contact measurement, it has been used in various fields. Some examples of using a 3D laser scanning technology to scan dangerous rock bodies are presented. The results show that the technology can perform well in the measurement of dangerous rock bodies and can overcome the shortcomings of traditional measurement methods.