Abstract: AnimagediagnosismethodbasedonthespectrumdiagnosiswasproposedtofacilitatetheinorbitdiagnosismeasurementofHallthrusterplume.Firstly，theRGBdatareflectingthespectralradiationintensityofdifferentwavelengthrangewasextractedfromtheplumeimagephotographedbythecamera.Basedontheanalysisofthecameraimagingprinciple，thecorrespondencebetweentheimagegrayvalueandspectralintensitywasdeduced.Thentheplumeimagediagnosismodelwasestablishedcombinedwiththespectralcollisionradiationmodel.Theexperimentalresultsshowthatthedistributionoftheelectrontemperatureandiondensityintheplumeregioncalculatedbytheimagediagnosismethodisinagreementwiththeresultsoftheprobemeasurement.Therelativeuncertaintyofthecalculatedresultsisabout20%and15%.Itisfurtherprovedthatthediagnosismethod，whichhasmoderateprecisionandhighreliability，issuitablefortheinorbitdiagnosismeasurementofHallthrusterplumeparameters.

Key words: Hallthruster, plume, imagediagnosis, spectralradiationintensity, grayvalue