Abstract: Cylindrical roller bearingelastic Jeffcott rotor system was studied. Critical rotational speed of the system was obtained through new calculating method of roller bearing stiffness and damping. The influences of bearing parameters as roller length, rotor mass and distance between bearings on the critical speed of the system were studied numerically．The influences of damping on critical speed were studied as well. A series of regular curves of the relation between the geometric parameters of system and the critical speed of system were obtained, and rounded analysis was carried on about the curves.