According　to　the　formation　parameters　of　No.3　coal　seam　in　the　Qinshui　Basin,　Shanxi　Province,　considering　the　interaction　between　seepage　and　deformation　in　the　borehole　wall　of　coal　seam,　the　stable　elastic-plastic　numerical　model　of　the　borehole　in　coal　seam　was　established　using　the　finite　element　method,　then　the　variation　of　pore　pressure　near　the　wellbore　wall　with　the　seepage　time　and　the　effect　of　time　delay　on　wellbore　stability　under　underbalanced　drilling　condition　were　studied.　The　variation　influences　of　maximum　displacement　and　maximum　plastic　deformation　around　borehole　wall　with　bottom　pressure　were　studied.　The　simulation　results　show　that　there　is　indeed　a　time　delay　effect　on　wellbore　stability　and　the　plastic　analysis　of　coal　and　rock　under　consideration　of　seepage　and　deformation　coupling　conditions　is　more　reasonable　and　effective,　and　it　provides　sufficient　time　conditions　for　guiding　drilling　construction.　©　Indian　Pulp　and　Paper　Technical　Association.　All　rights　reserved.