The　limit　states　of　a　primary　supporting　structure　were　used　to　represent　the　limit　states　of　the　tunnel,　and　the　analytical　methods　of　Catastrophe　Theory　and　bearing　capacity　were　respectively　used　to　determine　the　ultimate　displacement　values　of　the　tunnel.　The　calculated　results　indicate　that　the　ultimate　displacement　values　obtained　from　the　two　methods　are　close　to　one　another,　and　it　is　suggested　to　use　the　analytical　method　of　bearing　capacity,　which　is　with　explicit　mechanical　basis　and　small　values.　On　surrounding　rock,　the　effects　of　such　parameters　as　resistance　coefficient　and　side　pressure　coefficient　were　analyzed,　and　the　results　show　that　the　effects　of　two　parameters　on　the　ultimate　bearing　capacity　of　the　structure　are　great,　but　small　on　its　ultimate　displacement　values.　This　paper　proposed　the　determination　method　of　the　ultimate　displacement　values　of　a　tunnel.　The　method　directly　correlates　with　the　parameters　of　the　primary　supporting　structure　of　the　tunnel　and　is　with　explicit　and　reliable　calculated　results.　Therefore,　the　application　of　the　method　can　be　spread　to　the　determination　of　the　ultimate　displacement　values　of　a　tunnel　in　its　displacement　monitoring.　©　2022　IEEE.