Abstract: In order to accurately detect the existing underground gob in the boundary range of surface mine and to eliminate safety concerns,based on laser ranging a nd GPS positioning principle,the gob within the realm of Pinshuo surface mine had been fully detected by the cavity- autoscanning laser system. The results showed that th is system could san the gob quickly and safely through the drilling which from the surface to the empty area,which had the characteristics such as fully automatic,high spee d,high precision,simple data processing,etc. Through a comprehensive detection,the size parameters was implemented,which provided reliable basic data for underground gob stability evaluation and management of surface mine,and had great significance for guiding the surface mine production and protect the safety of the homework person nel and equipment.