In offline software of JUNO experiment, detector identifier (ID) and geometry management are indispensable parts. Detector identifier provides a unique ID number for every detector unit with readout, which is used by different applications in offline software. An ID mapping service is under development to provide associations between different sets of ID systems, including offline software, data acquisition, online event classification, electronics, detector testing and commissioning, etc. The geometry management system is developed based on Geant4 and GDML to precisely describe the detector details, such as geometrical structure, detector shapes, and positions. In offline software, the geometry management system provides consistent detector description information for different applications through interfaces between them.