Abstract: The Nanshan intrusion consists of monzonitic granite, granodiorite and tonalite, geochemically belonging to subduction type granite. The high precision LA-ICP-MS denudation plasma mass spectrometry (laser) single particle zircon micro area U-Pb isotopic dating yielded 446.1±3.5Ma, 447.2±5.3Ma, and 443.6±8.6Ma for monzonitic granite, granodiorite and tonalite, respectively, which indicates the Caledonian movement in the Qilian orogenic belt in the geological record. The rock-forming ages of the three different types of rocks may represent southward subduction of the Lajishan orogenic belt. The determination of the rock-forming epoch and tectonic environment of the Nanshan subduction type intrusion is of great significance for the tectonic evolution and dynamics mechanism of the Lajishan orogenic belt.