Abstract: For the complex geological conditions of the open-pit polymetallic mines transferring from underground mines and the limitation of a single geophysical exploration or drilling method，the complicate underground goafs and the unknown underground goafs usually can not be detected effectively，even not be detected at all，which greatly threaten the safety of open pit mining.Therefore，in view of the feature of the open-pit polymetallic mines transferring from underground mines，the geophysical exploration and the drilling method are combined to survey the goafs consecutively.That is，the distribution of the underground goafs is detected by synthetical geophysical method；the real location of the underground goafs is defined by engineering drilling survey；and the specific parameters of the underground goafs are gained by the Cavity Auto-scanning Laser System.The three methods above can ensure all goafs detected and explore all the complicate underground goafs and the unknown underground goafs.According to practices，it is proved that the complicate underground goafs and the unknown underground goafs all can be analyzed comprehensively and systematically by this synthetical probing technique，which provides a foundation for the underground goafs disposing by blasting，and then achieve to explore resources with potential danger in safety.

Key words: Open-pit polymetallic mine, Complicate underground goaf, Unknown underground goaf, Synthetical probing technique, Resources with potential danger