Objectives: Liaodong Peninsula is known to have been subjected to strong tectonism and magmatism which transitions from a compressional orogeny to extension and lithosphere thinning in the early Cretaceous. Previous researchers still have a disagreement on such a formation process. Methods: We performed the zircon SHRIMP UPb isotopic dating, in situ micro- area Lu- Hf isotope test, major elements and trace elements compositions of the monzonitic granite from Dajinshan Pluton of Liaodong Peninsula. Results: The crystallization age of the Dajinshan granite is 124 Ma, which belongs to peak period of the Early Cretaceous magmatic activity. The geochemical characteristics of the rocks show that Dajinshan granite is a kind of rock which experienced a high degree of crystallization process, belongs to weak peraluminous~peraluminous rock series. The Dajinshan granite is Itype granite which enriched with LILE such as Rb, Th, U and K; yet deficient on HFSE like P, Ti, etc, and Eu is medium negative anomalous. The zircon εHf(t) values of TW003 are between -25.8~ -14.2, TDM2 are between 2093Ma and 2805Ma. Conclusions: Dajinshan granite is the active continental margin arc granite formed by the Paleo Pacific plate subduction to the Eurasia plate. The lithogenous materials are the product of partial melting of mafic—ultramafic source rock in late Archean—Palaeoproterozoic lower crust, and mixed with felsic materials from upper crust during magma invasion. The Cretaceous extensional environment is influenced by the effect of the postorogenic extension and delamination of lower crust in the Liaodong Peninsula.