During　tunneling　process,　the　earth　pressure　in　chamber　must　be　maintained　balance　to　the　earth　pressure　on　excavation　face,　or　else　it　will　cause　the　ground　settlement.　Due　to　the　change　of　geology　and　working　conditions,　the　earth　pressure　in　chamber　is　usually　changed.　To　achieve　earth　pressure　dynamic　balance　control　in　chamber,　an　online　modeling　method　of　earth　pressure　in　chamber　is　proposed　based　on　LS-SVM.　A　sliding　time　window　method　is　introduced　to　update　the　sample　set　as　the　tunneling　process,　and　the　data　in　the　time　window　are　employed　to　establish　the　dynamic　model　of　the　earth　pressure　which　makes　the　model　refresh　online.　To　avoid　the　inversion　of　large　matrix,　the　recursive　algorithm　of　the　model　parameters　is　given　according　to　the　property　of　kernel　function　matrix　and　calculation　formulas　of　block　matrix,　which　makes　the　online　algorithm　of　LS-SVM　practical.　At　last,　the　simulation　experiments　are　presented　to　demonstrate　the　effectiveness　of　the　method　proposed,　and　it　is　more　suitable　for　the　earth　pressure　dynamic　balance　control　compared　with　standard　LS-SVM.　©　2013　ICIC　International.