The　failure　mechanism　of　tunnels　crossing　faults　is　a　critical　issue　for　tunnels　located　in　seismically　active　regions.　This　study　aims　to　investigate　the　nonlinear　response　of　rock　tunnels　crossing　inactive　faults　under　obliquely　incident　seismic　P　waves.　Based　on　the　equivalent　nodal　force　method　together　with　the　viscous-spring　boundary,　an　incident　method　for　the　site,　which　contains　fault　and　is　subjected　to　obliquely　incident　seismic　P　waves,　is　developed　first.　Then,　based　on　the　proposed　incident　method,　the　nonlinear　response　and　the　failure　process　of　the　tunnel　crossing　inactive　fault　are　numerically　studied.　The　numerical　results　show　that　the　failure　mechanism　of　the　tunnel　crossing　inactive　fault　can　be　attributed　to　the　combined　action　of　the　seismic　waves　and　its　associated　fault　slippage.　Finally,　parameter　studies　are　conducted　to　investigate　the　effects　of　the　wave　impedance　ratio　of　the　fault　to　the　surrounding　rock　and　the　incident　angle　of　P　waves.　By　the　parameter　analysis,　it　can　be　concluded　that:　(1)　with　decreasing　the　wave　impedance　ratio　of　the　fault　to　the　surrounding　rock,　the　seismic　response　of　the　tunnel　increases　significantly;　(2)　the　seismic　response　of　the　tunnel　increases　first　and　then　decreases　with　the　increasing　of　the　incident　angle　of　P　waves.　This　study　offers　the　insight　for　further　research　on　the　seismic　stability　of　tunnels　crossing　inactive　faults.