Abstract: Systemic studies of major elements and trace elements of the mafic dyke from Houcheng in Hebei Province indicate that SiO2=47.07%~50.28%, Na2O+K2O of the mafic dyke vary from 2.83% to 3.75%, LREE((La/Yb)N=4.40~4.86), with the enrichment of LILE（Rb, Th and U） and depletion of HFSE(Nb and Ta). The geochemical features of the mafic dykes show that they were derived from an intraplate extensional setting and experienced fractional crystallization of olivine+pyroxene+hornblende+biotite during the magmatic evolution. In addition, the La/Sm, Ta/La and Nb/La ratios suggest indistinct crustal contamination during the upward migration of the magma. Based on the ratios of trace elements and REE, the authors hold that the magma source belonged to transitional mantle. The parental magma of the maific dykes was formed in the garnet+spinel mantle with 10%~20% partial melting; moreover, the magma came from about 75km lithosphere mantle.