There are many Indosinian granitoids in the Songpan-Garze fold belt. Previous studies focused mainly on the eastern and central regions and made significant achievements. In this paper, Fangmaping-Sanyanlong granitic complex from the Jiu Long area, Southern Songpan-Garze fold belt have been studied, in order to further unravel the magmatism history and deep crust-mantle processes. Based on systematic field survey, petrographic and geochemical study, the granitic complex can be divided into two groups: Group 1 are high-K calc-alkaline rocks with adakitic affinities (C-adakites), with Sr>541×10-6，Y<12.4×10-6，Sr/Y>55, strongly fractionated REE patterns ((La/Yb)N>51) and high K2O/Na2O (≈1even>1)；Group 2 are ordinary calc-alkaline I-types with lower Sr (<450×10-6), higher Y (>17.4×10-6) and weakly fractionated REE patterns ((La/Yb)N<18). In general, group 1 is biotite monzogranite, while group 2 is biotite granite and granodiorite. The two groups have different Sr and Nd isotopic compositions (the group1 have ISr of 0.7066 to 0.7077 and εNd(t) of -4.43 to -3.96 while the group 2 have ISr of 0.7100 to 0.7123 and εNd(t) of -9.33 to -7.65) which indicates that their magma sources are distinct.Their formation conditions are also different. The residual phase of group 1 granitoids is possibly garnet-bearing amphibolite or amphibole eclogite, suggesting it formed in very high temperature and pressure setting, which implies its source region is very deep (>50km). The group 2’s residuum is possibly intermediate-basic granulite. The source region is shallower than that of Group 1 and the primary magmas were generated by partial melting of shallower lower crustal rocks. Using LA-ICP-MS zircon dating method, we obtained magma crystallization ages are 208±2 Ma for the Group 1 and 212±2 Ma for the Group 2. Combined with geological background, regional tectono-magmatic events and magmatism association, we suggest that lithospheric delamination can account for the magma generation of the Fangmaping-Sanyanlong granitic complex. C-adakite and ordinary calc-alkaline I-types are the products of partial melting of lower crustal and shallower lower crustal rocks, under this mechanism in post-collision setting.