Mesozoic granitoids in the middle and lower reaches of the Yangtze River were formed in the process of adjustment of lithospheric matters after the collision of North China and Yangtze craton. Systematic studies of Sr, Nd, Pb isotopic data show that the two stages of granitoids are characterized by similar magmatic sources and the existence of crust crust mixing. In the crust crust mixed magmatic sources, the main mixing members may be the source rocks of the granitoids in DL and YZL lithozones, the former equal to high grade metamorphic rocks in Dabie complex and the latter being the basic and intermediate basic meta igneous rocks which underplated and midplated into the lower crust during Pt2-3 and the Pt1 sedimentary volcanic rocks in the Yangtze cratonr. Those characteristics indicate that the lower crust in the middle and lower reaches of the Yangtze River was tectonic melange belt between Dabie block and Yangtze block during the Mesozoic collision of the two blocks. Two different substances formed finger like connection texture in the lower crust of YZC block (the middle and lower reaches of the Yangtze River).