Press-pack　insulated　gate　bipolar　transistor　(IGBT)　is　widely　used　in　transmission　systems　due　to　its　high　reliability　and　short-circuit　failure　modes.　However,　there　is　a　lack　of　research　on　the　failure　mechanism　of　elastic　press-pack　IGBT.　For　the　elastic　press-pack　IGBT　sub-module,　based　on　the　principle　of　electrical　measurement,　this　paper　designs　a　power　cycling　test　system　for　power　cycling　test　and　thermal　resistance　measurement.　Based　on　the　structure　function　method,　the　changes　of　electrical　properties　and　thermal　resistance　after　power　cycling　are　studied.　The　reliability　and　failure　mechanism　of　the　elastic　crimp　IGBT　sub-module　are　analyzed,　and　the　conclusion　that　the　gate　oxide　layer　damage　is　the　main　failure　principle　is　obtained.　The　work　of　this　paper　fills　the　gap　in　the　practical　application　of　elastic　press-pack　IGBT.