Abstract: Traditional detection approaches are difficult to obtain the actual spatial shape of the complex empty areas due to the limits of detection technology. It poses many problems for further analysis and treatment with empty areas.Using the 0~2 line of the empty areas of Longqiao iron ore as the case, this paper performs laser scanning on it with 3D laser detection system (C-ALS). The data on the shape, size and space position of the empty area are obtained by establishing a 3D geological model with Surpac software. The falling height of overburden rock of the empty area and causes are analyzed. The results show that: the actual height of the empty area is almost equal to the theoretical height values. And this section of roof strata has no falling tendency.