This paper describes the analysis and measurement of the dynamic motions of a large-scale rotating roll workpiece, which is used for a large-scale lathe, under the gravity condition. A dynamic model which includes the gravity effect was first established. In order to investigate the behavior which comes from stiffness differences of the journal bearing at the headstock and the tailstock, a spring-mass-damper system was also established. In addition to the simulations, the behavior of the rotating roll workpiece was investigated with respect to the different rotating speed. In the experiment, a mirror finished hollow type roll workpiece with a diameter of 320 mm, a length of 1800 mm, a weight of about 340 kg was fabricated by a large-scale lathe. Five capacitive type displacement sensors were mounted on the sensor holders which were arranged along the axis of rotation of the spindle. The behavior measurement was carried out at 5 sections of the roll workpiece along the axial direction. The rotating speed was set to be 5, 50, 100, 150, 200, 250 and 300 rpm. The dynamic model for the analysis with simulations and the measurement result of the behavior of a rotating roll workpiece according to the different rotating speed are presented in this paper.