With the development of the in situ zircon SHRIMP U-Pb dating method and laser ablation ICP-MS, the study of the age distribution of detrital zircons from sedimentary rocks has become an effective way to find the source area of clastic material and also become an important topic all over the world. However, during zircon laser ablation (LA)-ICPMS dating, the U-Pb isotopic fractionation remains one of the principal obstacles for precise zircon dating. The experiments performed by the authors demonstrate that a low laser frequency (5 Hz or 6 Hz) would reduce element fractionation during laser ablation. The U-Pb ages of international zircon standards GJ-1 and the laboratory zircon standard SK10-2 were measured by LA-ICP-MS in 20 μm spot size at 5 Hz laser frequency. The reduce mean 206Pb/238U ages obtained in our analysis are in good agreement with the published values. Quartz sandstone from Changlongshan Formation of Qingbaikou System, the oldest metasedimentary rock in Liujiang area of Qinhuangdao City, was deposited unconformably on the Neoarchean potassic granite. Detrital zircons from the quartz sandstone have 207Pb/206Pb ages of 2635 Ma to 2487 Ma. A comparison with the Beiijng-Jixian stratatigrphic section, from Early Proterozoic, the study area experienced a long period of weathering and erosion, and then began to deposit on the surface and become the source area of clastic sediments of the Changlongshan Formation until the early Neoproterozoic. Hf isotopic compositions of the detrital zircons indicate that the clasts were main-ly derived from the reworked ancient crust, suggesting that the mass of the continental crust was largely established at ～2.5 Ga in its source area.