According　to　the　provisions　of　the　Chinese　Code　for　Seismic　Design　of　Buildings　(GB　50011-2010),　the　anti-seismic　capability　of　a　frame　structure　in　two　horizontal　directions　are　designed　respectively.　However,　earthquake　action　is　multi-dimensional　and　random,　which　will　make　a　panel　zone　in　a　frame　structure　be　loaded　by　bidirectional　actions　at　the　same　time.　Thusly,　its　anti-seismic　capability　may　be　lower　than　the　designed　capability　based　on　a　unidirectional　earthquake　action.　So　far,　the　detailed　calculation　methods　of　shear　capability　for　a　panel　zone　in　a　reinforced　concrete　(RC)　frame　subjected　to　bidirectional　loading　have　not　been　reported.　In　this　work,　the　shear　mechanism　of　a　panel　zone　in　a　RC　frame　under　bidirectional　loading　was　analyzed.　It　demonstrated　that　a　synthetic　shear　force　is　imposed　on　a　panel　zone,　the　oblique　compression　zone　comes　into　being　at　the　end　of　a　panel　zone,　and　the　diagonal　strut　is　formed　in　a　panel　zone,　which　is　different　from　the　shear　mechanism　under　unidirectional　loading.　A　shear　capacity　calculation　model　was　established　based　on　the　strut　and　tie　model,　and　the　predicted　values　by　this　work　are　in　a　good　agreement　with　the　reported　experimental　results.　©　2019,　Engineering　Mechanics　Press.　All　right　reserved.