In　the　simulation　of　cross-type　terahertz　bandpass　filter　by　using　the　finite-difference　time-domain　method,　the　main　peaks　narrow　as　the　thickness　of　the　A1　foil　increases,　and　several　abnormal　transmission　peaks　appear　at　high　frequencies.　A　terahertz　filter　with　A1　foil　thickness　of　150　f/m　is　fabricated　by　femtosecond　laser　micro-machining;　it　is　tested　using　a　time-domain　terahertz　spectroscopy　system.　The　results　show　that　the　experimental　results　are　consistent　with　the　finite-difference　time-domain　method　simulation　results.　The　anomalous　transmission　peaks　result　from　the　Fabry　Perot　resonant　coupling　of　the　surface　plasmon　polariton　waves　on　the　sidewalls　of　the　slits　of　the　cross　structure.　This　coupling　effect　may　be　useful　in　controlling　surface　plasmon　polariton　waves　and　fabricating　new　terahertz　devices.　©　2019　Universitat　zu　Koln.　All　rights　reserved.