3D　optical　storage,　spatially　expanding　storage　capacity,　is　regarded　as　an　effective　and　economical　way　to　break　the　diffraction　limit　of　the　conventional　2D　optical　storage.　In　this　study,　a　new　kind　of　3D　optical　storage　medium,　i.e.,　vanadium　ions　(V5+)　doped　sodium　borate　glass,　is　developed,　showing　intriguing　spatially-selected　photochromism　(PC)　upon　laser　driven　excitation.　Significantly,　a　brand-new　PC　mechanism　of　V5+-aggregation　regulated　by　localized　optical　basicity　(OB)　of　glass　is　proposed　and　demonstrated.　The　developed　PC　glass　is　responsive　to　a　low-price　desktop-level　mini-laser　to　encode　optical　information,　yields　unique　twofold　decoding　modes　in　bright-　and　dark-fields,　and　shows　good　data　erasibility.　3D　volumetric　optical　storage　with　a　memory　density　of　≈480 Mbit cm−3　is　realized　with　the　aid　of　an　advanced　femtosecond　laser　micro-machining　system.　The　findings　suggest　a　novel　design　approach　to　fabricate　3D　PC　glass　in　terms　of　manipulating　the　scale　of　optical　basicity　in　glass,　hopefully　stimulating　the　development　of　new　multi-dimensional　PC　optical　storage　media.　©　2023　Wiley-VCH　GmbH.