Abstract: In this Paper, an analysis is made of the change of geological behaviours of faults during the change of their mechanical properties, with the Luntai listric fault in the northern Tarim Basin which was first a thrust fault and converted later into a normal fault as an example.It acted as a passageway for oil and gas when it was converted from a shear fault into a tensile fault, and conversely as a seal to block off oil and gas when it turned from a tensile fault to shear fault, and the associated rollover anticline may become an oil trap.The proposed oil-control model as indicated by oil-gas preservation in sediments overlying a fault may also be applicable to those in eastern China.