Abstract: The study fault,discovered by aeromagnetic measurement,is the largest in eastern China.There has been some argument about how the fault extends to the north.Aeromagnetic and gravitational data show that the fault goes through Bohai,Anshan and Shenyang,to the Yilan-Yitong fault straight away.The magnetic field in depth shows that the northern segment of the fault is very different from the intermediate one as the fault passes by Anshan;the intermediate,for example,goes down to the very depth,on the both sides of which are different characterized basements which are boundary planes between the crustal structures with different substances;the northern does not extend so deeply as does the intermediate,making little sense to controlling of composition of substance.It is inferred from available data that the age for the generation of the northern segment of the main fault corresponds to Indosinian Period and the magmatism in this area is governed by the faults trending northwest.And the intermediate segment may have been formed in the late Archeozoic-early Proterozoic time.