Permian to Triassicis an important turning point of geological history during the transition period of Paleozoic to Mesozoic, in which the largest mass extinction events in geological history happened. As the transition stage of Permian to Triassic, the era of Shiqianfeng Formation is crucial to define the boundary of Permian to Triassic. In order to determine the era of Shiqianfeng Formation in Xishan, Taiyuan, North China, the laser ablation multi collector inductively coupled plasma mass spectrometry (LA MC ICPMS) was applied to date the U Pb age of detrital zircon. Four sandstone samples (SNF, XM, K8, LJG) from the marker layers of strata division and correlation from the Xiashihezi Formation, Shiqianfeng Formation and Liujiagou Formation were analyzed. Four sandstone samples SNF, XM, K8, LJG obtained youngest graphical detrital zircon age were 270 Ma, 296 Ma, 250 Ma, 262 Ma, respectively. The results show that the deposition time of Shinaofeng sandstone(SNF) was not earlier than 270Ma, the deposition time of K8 sandstone(K8) was not earlier than 250Ma. Therefore, Shiqianfeng Formation of Xishan, Taiyuan should belong to the Lower Triassic, and the boundary of Permian to Triassic lied under the K8 sandstone. Symbol`@@