Abstract: The abnormal formation overpressure in the western part of southern fringe of Junggar Basin mainly existed in the secound and third row of structural zones in northern Tianshan piedmont fold zones,and were characterized by regional zonal distribution.According to drilling data revealed,formation overpressure were characterized by "strata-control and time-control",which showed that the depth of the top surface of abnormal overpressure was controlled by Anjihaihe formation (E₂₊₃),and its 3-D shape was a irregular box,which has the character of overpressured compartment.And its forming mechanism is "polygenetic",which was formed by superimposing of sedimention and tectonic.