Taking　the　construction　of　a　shield　metro　tunnel　with　small　clear　spacing　as　an　example,　the　variation　law　of　secondary　stress　on　advanced　tunnel　segments　caused　by　later　tunnel　excavation　during　construction　of　parallel　shield　tunnel　with　small　clear　spacing　is　revealed　by　analyzing　the　field　monitoring　data.　By　using　of　FLAC3D　finite　difference　numerical　simulation　software,　the　numerical　simulation　is　carried　out　for　the　construction　of　parallel　double-tube　tunnel　with　different　clear　spacings　and　a　comparative　analysis　of　simulating　values　and　monitoring　values　of　secondary　stress　is　conducted.　It　is　concluded　that(1)the　secondary　stress　is　sharply　varied　as　the　later　excavated　tunnel　approaches　to　monitoring　section.　The　circumferential　stress　is　loaded　at　horizontal　diameter　and　the　magnitude　of　circumferential　stress　is　larger　than　longitudinal　stress.　The　top-half　on　the　left　side　of　tunnel　is　the　most　loaded;　(2)　the　change　law　of　monitoring　values　of　secondary　stress　is　generally　similar　to　the　change　of　simulating　values,　showing　that　later　excavated　tunnel　has　an　obvious　influence　on　stress　distribution　in　advanced　tunnel.　With　decreasing　of　clear　spacing,　the　magnitude　of　circumferential　secondary　stress　is　gradually　increasing;　(3)　the　numerical　simulation　indicates　that　stress　concentration　appears　since　the　clear　spacing　gets　smaller.　©,　2015,　Editorial　Office　of　＇Modern　Tunnelling　Technology＇.　All　right　reserved.