The dynamic model of the pedestal looseness fault rotor-bearing system with slowly varying mass was set up. The complex characteristics of the rotor-bearing system were numerically studied. Along with the increase of the looseness mass, the chaotic motion area and amplitude range increase in the region of critical rotating speed; and P-3 motion area disappears in the region of twice-critical rotating speed, chaos is the main motion form. Along with the increase of the coefficient of mass slowly varying amplitude, the instable rotating speed increase, and the chaotic motion area decreases, P-n motion area increases in the region of critical rotating speed and twice-critical rotating speed. The conclusions may provide basis reference for fault diagnosis.