By using a simplified rotor finite element model，comparative analyses with and without load reduce device (LRD) design were carried out

including the critical speed

dynamic load response and the axis trajectory of the rotor. The mechanism of structural load reduction under fan blade out was studied. Analysis results indicated that due to the fuse design of the 1# bearing

the low-pressure rotor support changed from three bearings to two bearings.As a result

the critical speed of fan mode was reduced

the radius of axis trajectory was decreased

and fan rotor ran at supercritical speed

which reduced load response at high speed.The method adopted in this mechanism study can be used to determine the load threshold range of fused structure and to evaluate its load reduction effect.