In order to study the age, geochemical characteristics and tectonic genesis of the ore-bearing intrusions of Dasuji porphyry Mo deposit, three kinds of rock samples of quartz porphyry, syenogranite and granite porphyry that are related to molybdenum mineralization were collected from the deposit. Zircon U-Pb dating reveals that the ages of quartz porphyry, granite porphyry and syenogranite are 231, 227 and 225 Ma, respectively. Characteristics of major and trace elements indicate that they belong to high-K calc-alkaline to shoshonite series and highly fractionated I-type granite. Geochemistry of the rock associations, integrated with regional geology indicate that Dasuji area was in extension during Indosinian. The upwelling of asthenosphere triggered partial melting of crust in a wide range of depth. Magma related to this deposit was generated in this process. During ascending, the magma extracted ore elements from protore which had collected ore elements in the pre-Mesozoic during multiple geological activities and the magma became more enriched in Mo due to the extensive crystal fractionation. When volatiles in magma were supersaturated, ore-forming fluid was separated from melt with Mo. Ore minerals were mainly precipitated with quartz and filled in the fractures during the boiling process.