A　mechanical　model　for　shear　bearing　capacity　of　buckling　restrained　steel　plate　shear　walls　was　developed　based　on　their　stress　distribution.　It　was　considered　that　the　shear　bearing　capacity　was　provided　by　the　effective　shear　field　of　the　panel　and　edge　support　members.　A　uniform　formula　for　shear　bearing　capacity　of　buckling　restrained　steel　plate　shear　walls　was　developed　and　validated　by　comparing　with　experimental　and　numerical　results,　and　the　specification.　Further　analysis　shows　that　in　range　of　practical　aspect　ratios　of　0.5-2.0,　the　effective　shear　area　varies　in　20%-55%　of　the　whole　panel　of　the　shear　walls　connected　with　only　beams,　and　the　bearing　capacity　is　reduced　by　10%-52%　compared　with　that　of　the　walls　connected　with　both　beams　and　columns.　Its　safety　margin　is　lower　than　that　of　the　walls　connected　with　beams　and　columns　and　the　walls　with　added　side　columns　because　of　tearing　at　the　corners　in　advance.　The　feasibility　of　adding　columns　at　both　vertical　edges　of　the　walls　connected　only　with　beams　was　illustrated　by　an　example.　The　requirement　of　side-column　section　areas　was　proposed　to　ensure　an　effective　shear　stress　field　in　whole　panel.　©　2017,　Editorial　Office　of　Journal　of　Building　Structures.　All　right　reserved.