The invention relates to a pivot joint structure of the motor rotor including a spindle and a snap ring. The spindle is centrally disposed in the rotor and the end thereof near the urging part has a scoop channel with smaller outer diameter. The urging part has at least one plane surface along the axial direction and the cross section is formed in a non-circular shape. The center hole of the snap ring takes the shape corresponding to that formed by the cross section(s) of the urging part and the gap therebetween provides a minimum space for the inserting in the urging part. Consequently, regardless of the assembly or disassembly of the rotor, the snap ring structure won't be affected and the deformation or fracture thereof won't take place.