Abstract: In view of pedestal looseness fault often occurred in the engineering,a finite element model with looseness fault was established and dynamic characteristics of one-support looseness and two-support looseness were studied.The results show that the system motion experiences period-one,period-two,period-six and period-four with the decrease of looseness stiffness in two looseness cases.However,the rotor trajectory is different,since one-support looseness,rotor trajectory is an 8 shape curve with large difference in up and down layers,then becomes two nested 8 shape curves,finally becomes a spiral shape curve.For two-support looseness,rotor trajectory is approximately triangle,then two adjoining 8 shape curves,and finally becomes a spiral curve.The results will provide theoretical references for fault diagnosis,dynamic design,and safe operation of rotor-bearing system.