Based　on　the　calculation　diagram　specified　by　the　current　codes,　the　slip　angle　was　introduced　and　the　modified　calculation　model　was　proposed,　in　which　the　potential　slip　plane　deflects　along　with　the　change　of　parameters.　The　surface　boundary　condition　was　considered　by　using　the　horizontal　slice　method,　so　that　the　slip　angle,　the　fracture　angle,　the　lateral　resistance　and　the　vertical　ground　pressure　were　calculated　in　a　more　accurate　way　by　graphical　method.　The　case　with　different　ground　conditions　was　studied.　Furthermore,　the　influences　of　anti-shear　indices　on　the　block　volume,　the　lateral　resistance　and　its　distribution　pattern,　and　the　vertical　ground　pressure　were　discussed　through　sensitivity　analysis.　The　results　show　that　the　calculation　results　from　traditional　model　and　modified　model　fit　each　other　well.　The　modified　model　can　be　degenerated　into　the　traditional　model　on　the　same　calculation　assumptions.　The　ground　stability　is　enhanced　with　the　increase　of　cohesion　and　friction　angle,　which　reduces　the　volume　of　triangle　block　and　the　lateral　resistance.　Meanwhile,　the　influence　of　gravity　on　the　distribution　pattern　of　lateral　resistance　is　weakened,　and　the　influence　of　anti-shear　indices　is　relatively　enhanced,　which　makes　the　centroid　of　distribution　curve　move　up.　Therefore,　the　synergistic　effect　provided　by　the　decreased　lateral　resistance　and　the　increased　volume　of　trapezoidal　block　enhances　the　vertical　ground　pressure.　Cohesion　and　friction　angle　affect　the　calculation　of　ground　pressure　in　an　identical　mechanism,　so　that　the　equivalent　friction　angle　can　also　be　adopted　to　calculate　the　ground　pressure　of　shallow　tunnel.　©　2022　Central　South　University　of　Technology.　All　rights　reserved.