Grounding　grids　are　widely　used　in　substations　to　maintain　the　safe　operation　of　operators　and　power　apparatus.　In　this　paper,　an　electromagnetic　ultrasonic　technique　is　proposed　to　diagnose　the　degradation　of　grounding　grids.　Firstly,　the　propagation　of　guided　waves　in　an　infinite　plate　is　studied.　It　is　shown　that　the　lower　shear　horizontal　wave　(SH0)　has　several　unique　features　that　are　attractive　for　long-range　non-destructive　testing　(NDT).　Secondly,　the　propagation　of　guided　waves　in　a　rectangular　section　bar　is　investigated　experimentally.　It　is　found　that　the　SH0　wave　excited　by　an　electromagnetic　acoustic　transducer　(EMAT),　compared　to　a　Lamb　wave　excited　by　a　piezoelectric　transducer,　has　a　more　powerful　transmission　capability　in　a　rectangular　section　bar.　Thirdly,　SH0　wave　experiments　are　conducted　on　plates　with　different　widths:　it　is　found　that　the　variation　in　width　has　little　influence　on　the　propagation　of　the　SH0　wave　when　the　width　of　the　plates　is　greater　than　the　width　of　the　EMAT　transducers.　Fourthly,　experiments　are　conducted　on　a　rectangular　section　bar　in　the　laboratory　to　investigate　the　sensitivity　of　the　SH0　wave　to　defects　and　the　surrounding　environment.　It　is　found　that　SH0　wave　testing　offers　an　effective　way　to　evaluate　the　health　condition　of　a　rectangular　section　bar.　Finally,　the　proposed　technique　is　applied　to　the　NDT　of　a　grounding　grid　in　the　field.