The Mengdong GroupComplex is a series of Precambrian metamorphic sedimentary and magmatic complex cropped out in the Laojunshan area，southeastern Yunnan Province. For its peculiar location， the Mengdong GroupComplex has the important scientific significance to understand the tectonics of SE Yunnan，and even of South China and Tethys. In order to probe the metamorphism and deformation characteristics，by means of microscale observation such as optical microscope， electron microscope and electron probe，etc.，the characteristics of metamorphicdeformation have been studied in details. The results show that the macro styles of the Mengdong GroupComplex contain fold bedding，syntectonic secrete crystal veins，asymmetric shear lens，decollement subductile structures，and the micro structures consist of mica fish，kink，quartz rectangular bank. Microscopic structure statistics data indicate that the Mengdong GroupComplex experienced the squeezing and stressing process in the directions of NESW，SENW，EW and SN，of which the result is similar to macro and micro structure.Meanwhile，the temperature of garnetbiotite mineral pairs in schist is 429℃ in average and the pressure of the schist is 0.5GPa. The temperature of tourmalinebiotite temperature in gneiss is 546℃ in average，corresponding to typical assemblages of the high green schistlow amphibolites facies. The UPb dating of titanite and rutile mineral suggests that the major metamorphism and deformation events occurred around ca. 236Ma and 170Ma.The above evidence shows that the Mengdong GroupComplex has experienced many metamorphicdeformation， and the principal stress of metamorphicdeformation （SENW） controls macrostructure framework of metamorphic GroupComplex（236Ca.）， but SN and EW may be the directions of the substrain matched with the principal stress and NESW may be another direction after main metamorphicdeformation and age is confined to 170Ma. On behalf of the Laojunshan dome of early Yanshanian extensionalshear activity. Combined with other geochronological data，the Mengdong GroupComplex had undergone successively the largescale thrust events in early Indosinian，the extensionshearing events in later Indosinian and early Yanshannian，and the contact metamorphism in later Yanshannian. Based on the study above， it can be outlined that the dynamic background of these metamorphicdeformation events is the Indosinian event, which is controlled the main features of the Mengdong GroupComplex. Laojunshan uplift of the dome began to activate in 236Ma，in consistent with the time of Tethys closure and collision, and stretched to 170Ma，after collapse of dome. NE directions widely developed klippe and offsite rock in Indosinian WenshanMalipo imply that preIndosinian formation belongs to the Mengdong GroupComplex and should be a set of foreigner rocky Nappe from Northern Vietnam. Therefore, the above results provide evidence for the study of tectonic evolution in the west of South China.