Abstract: There existed Late Cretaceous magmatic activity in the Baoshan block, western Yunnan Province. The origin of magmatic rocks, source area properties and geodynamic background are not clear. The whole rock geochemistry and zircon U-Pb geochronology of Late Cretaceous granites in the Caojian complex granite exposed to the northern Baoshan block were studied in this paper. A sample LA-ICP-MS zircon U-Pb isotope dating result is 68.8±1.2Ma (MSWD=3.3, n=12), indicating age information of Late Cretaceous. The whole rock geochemical study shows that the Late Cretaceous granite in the Caojian complex granite body is the S type granite of high silicon (SiO₂=69.72%~76.09%), rich potassium (K₂O=4.63%~6.65%) and peraluminous nature (A/CNK=1.06~1.16). The magma was formed from the partial melting of the argillaceous rocks in the central part of the continental crust with the residual facies being granulite, and the residual facies is mainly composed of plagioclase+hornblende+garnet. There existed many peraluminous granites in the Late Cretaceous to Paleogene period in the Baoshan massif. Some experts believe that these granites might have been formed by the thickened crust in the inland of the Baoshan massif during the eastward subduction of the new Tethys oceanic plate, but the time limit for the start of the subduction of the new Tethys Ocean is controversial, and it was probably formed later than the formation of this period of granite. It is believed that the Late Cretaceous granites in the Baoshan massif may be under the regional extension background of the global distribution pattern of the global pan Gaia formed by the Indosinian movement. The deep heat flow (mantle material) migrated upward with the addition of water-containing fluid from the crust. These factors caused partial melting of the central crust. The geochemical characteristics of the rock mass are the reflection of the magma source area rather than the tectonic background of magmatic production.