The clustering debris flows on June 15, 2021 in Rongxia Gorge was one of the catastrophic geo-hazard events in southern flanks of Himalayas. Presently, the debris flow source activity has been not examined yet. In this work, the debris flow sources were identified by the pre-event GF-1B and post-event BJ-2 high resolution images, multiple images were used to derive the glacier lake change and the ground surface deformation during 2000-2021 were obtained by SBAS-InSAR method. The results show that deformation sites on right terrain are more than the left terrain, and the velocity shows more rapid increase. The deformation sites at left terrain were in the coniferous forest zone, shrub and meadow area, while the deformation sites at right terrain were in the meadow cushion vegetation and lichen area. The ground surface deformation exhibits subsidence in spring and summer season, while heave in autumn and winter, while the subsident exceeds heave totally. For the debris flow material resources, the landslides in the tributary head, on planar and convex slope, and on channel banks all share similarities in seasonal changes, while the subsidence exhibits in decreasing order of upper part, frontal part and the head scar area. Such deformation changes may result from landslide frontal part attraction and pushing from the back part. The rocky glacier shows obvious seasonal heave and subsidence deformation and the center part deforms greatly. Additionally, the Yalongcuo Glacier lake area has increased about 43 percent since 2000 and the lateral moraine bank shows great deformation. The results of this work could contribute to the geo-hazard prediction in some alpine and humid regions of southern flanks of Himalayas.