Proterozoic magmatic rocks are seldom reported in the southwestern margin of the North China craton, but the K feldspar granite porphyry and altered diabase distributing along the Liupan fault belt in the Tiemahe section in Baojiashan of Longxian County in southwestern margin of the North China Craton are formed in Early Proterozoic. The K feldspar granite porphyry is characterized by rich potassium (Na2O/K2O=1.66~3.36), Calc alkaline and metaluminous to weakly peraluminous（A/CNK=0.85~1.18）series. It shows a LREE enrichment pattern, a obvious differentiation between LREE and HREE（LREE/HREE=4.08~12.03）and significantly negative Eu anomalies(δEu＝0.50~0.53). The trace element geochemistry is characterized by enrichment of large ion lithophile elements K, Rb, Ba, Th and depletion of high strength field elements Nb, Ta, Ti, Hf; P and Sr depleted extremely. The K feldspar granite porphyry has higher ratios of Rb/Sr and Ga/Al, and exhibits characteristics of A type granitic rocks. Zircon U Pb LA ICP MS ages of two samples of the granite porphyry are 1814±12Ma and 1781±12Ma respectively. According to regional geological data，the Southwestern Margin of North China Plate in Paleoprotozoic is under the strongly extensional setting and probably related to the Helan aulacogen's southwards.