Inthispaper,theanalysisoftheoccurrenceandthedevelopmentoftyphoonandtropicalcycloneismadewiththeunstabletheoryofwave.Theresultindicatesthattheprimarywaveistheunstableinertia-gravitywaveintheprocessoftheoccurrenceandthedeveJopmantoftyphoonandtropicalcyclone:Theexistenceofthedeepmoistlayerandtheheatingbymoisturecondensationcanimpelandintensifytheunstabilityofthewaveandisfavourableforthereductionofthewaveenergydispersion,therefore,itisgoodfortheformationandthedevelopmentoftyphoonandtropicalcyclone,andalsocanslowdownthewavespeed.Besides,theconditionthatthechangeofthespecificvolumeofthebasicstatewithpressureislessthanthatofadiabaticstatemayalsoleadtothewaveunstability,thusmayhavecertaineffectontheoccurrenceandthedevelopmentoftyphoonandtropicalcyclone.
