The paper studies monazite and zircon U- Pb geochronology, chemistry of the gneissic monzogranite and biotite plagiogneiss inclusions, which intrude into the Longshan Group in the joint site of the Qinling—Qilian orogenic belts. The gneissic monzogranite are characterized by the geochemical feature of I- type granite, and the age of 433. 5 ± 1. 8 Ma is given by means of LA- ICP- MS monazite U- Pb dating, and the three peak ages（439. 5 Ma、634. 5 Ma and 2265 Ma）and five sub- peak ages（568. 7 Ma, 1875 Ma, 2112 Ma, 2604 Ma and 2738 Ma）are given by means of LA- ICP- MS zircon U- Pb dating. The geochemical features of the biotite plagiogneiss inclusions suggested that its protolith should be the meso—basic magmatite suffered from remarkably crystallization differentiation, and two types of zircons are selected: ①Magmatic zircon with clear oscillatory zoning and suffered from hydrothermal alteration, and LA- ICP- MS zircon U- Pb dating obtains a nice line of inconsistency with the upper intercept age（2194 ± 42 Ma）and the lower intercept age（431. 2 ± 58. 1 Ma）, ②Metamorphic zircon and（or）hydrothermal alteration zircon without oscillatory zoning and gloomy CL image, and LA- ICP- MS zircon U- Pb dating obtains peak age of 513. 1 Ma. Combined with regional geological data, the formation age of the gneissic monzogranite is defined as 439. 5~431. 2 Ma, and the formation age of the biotite plagiogneiss inclusions is defined as 2194 ± 42 Ma. The formation age of the gneissic monzogranite is basically coincide with that of the surrounding rock（plagioclase amphibole schist）revealed in the literature, and it is suggested that intermediate—basic and acid magmatic activities broadly developed during 439. 5~431. 2 Ma in the Longshan area, and the significant regional difference of change of magmatism exists at that time. The northward subduction of the northern Qilian Ocean and the western segment of the northern Qinling Ocean had affected the studied area in 513. 1 Ma. The peak ages of 2738 Ma, 2604 Ma, 2265~2112 Ma and 1875 Ma should correspond the continental crustal growth at the end of Neoarchean and the craton splitting at the early stage of Paleoproterozoic of the North China craton. During the period of 634. 5 Ma, the studied area should be in relatively special tectonic setting which is poorly known so far. In total, the Longshan structural belt evolved as a part of the North China Block during Precambrian period, and its tectonic evolution process has been significantly influenced by the Qinling orogenic belt and the North Qilian orogenic belt since the Phanerozoiceon.