Meta_sedimentary rocks comprising sillimanite_garnet_biotite gneisses and mica schist are cropped out in the middle_north segment of Ailao Mountain me tamorphic complex belt. Petrographic observation reveals that the sillimanite_ga rnet_biotite gneisses experienced amphibolite_granulite facies metamorphism and subsequent retrogressive superimposition. Traditional thermobarometry (GB_GASP) was applied to constraining p_T conditions of the mineral assemblage at each metamorphic stage. The mineral assemblage of the peak stage (M₁) is character ized by Grt+Sil₁+Bt₁+Kfs+Pl+Qtz+Ilm, recording p_T conditions of 690~7 50℃ and 690~810 MPa. The near_isothermal decompressional stage (M₂) is disti nguished by the directional alignment of all metamorphic minerals, with typical dehydration reaction being 2 Bt→Sil+6 (Mg, Fe)O+K₂O+5 Qtz+2 H₂O, and minera l assemblage is characterized by Grt+Sil₂+Bt₂+Kfs+Pl+Qtz+Ilm, formed un der p_T conditions of 650~720℃ and 450~630 MPa. The mineral assemblage of the retrograde stage (M₃) is composed of Bt+Ms+Qtz+Pl, suggesting p_T con ditions of 580~640℃ and 400~500 MPa. The metamorphic evolution is characteriz ed by an isothermal decompressional clockwise p_T path, revealing a subducti on and continent_continent collision process between Indian and Yangtze blocks, following a tectonic exhumation accompanied by high temperature strike_slip shea ring and biotite dehydration_melting.