Abstract：Under the restriction of geological conditions and detection technology，accurate data of real space shape of complicated cavity are very difficult to obtain with conventional detection methods. The cavity data detected by these methods are so rough for building model in numerical analysis；and high reliability of stability analysis based on the model can not be reached. Therefore，3D laser scanning for complicated cavity with cavity auto scanning laser system(CALS) is put forward. This system is capable of being inserted into voids and cavities via predrilled boreholes to quickly and safely survey old workings；after exact 3D point cloud data are obtained by using CALS，the data can be processed so as to accurately simulate 3D geological model of the cavity in Surpac software；and then，adopting coupled Surpac-FLAC3D technology，numerical analysis model with real space shape of the cavity is created in FLAC3D，and the stability calculation is conducted in the final phase. Selecting the underground cavity of Sandaozhuang open-pit mine as an example，real space boundary of the irregularly cavity is scanned and 3D block model of the surrounding rock is modelled using the method mentioned above；following that，coupled Surpac-FLAC3D technology has been studied and 3D model data is successfully introduced into FLAC3D software；combining mechanical parameters of surrounding rock based on field tests and other geological conditions，static calculation is performed. According to the calculation results，stability of the cavity is analysed referring to the nephogram of stress and displacement of the surrounding rock，and the accuracy and reliability of the analysis results are greatly improved.
