A　field　monitoring　programme　is　carried　out　for　the　open-excavated　project　of　a　subway　station　in　Beijing,　the　trends　of　the　displacements　and　the　inner　forces　are　under　control,　and　the　change　of　characteristics　of　displacements　and　inner　forces　in　the　retaining　structure　during　the　construction　is　analyzed.　The　necessary　engineering　measurements　are　taken　to　keep　the　stability　of　the　excavated　foundation　pit.　There　are　several　monitoring　conclusions　as　follows:　a)　the　horizontal　displacements　of　retaining　structure　increase　with　the　construction　duration　and　tend　to　be　able　gradually　after　the　foundation-pit　excavation　is　completed,　The　largest　displacement　appears　on　the　second　layer　steel　support　tube　and　the　displacement　is　the　smallest　in　the　bottom　of　retaining　structure;　b)　the　axial　forces　on　the　first　layer　steel-support　tube　significantly　greater　than　those　of　the　second　and　the　third　layers;　and　c)　the　axial　forces　on　the　diagonal　steel-support　tubes　in　the　outside　corner　of　the　foundation-pit　are　much　greater　than　those　of　the　others.