Die-less spinning can achieve the thin-walled parts with the regular shape of cone and cylinder or even some non-axisymmetric shapes. And it has advantages in forming some difficult demolding shapes. In this study, dieless spinning in a cone-cylinder combined hollow part and its forming mechanism were investigated. A ballcrown-shape roller was used to replace a conventional roller in the spinning process. The roller movement and spindle rotation were controlled by a computer numerical control spinning machine to achieve a planned roller path. The pass sets of tilted and horizontal lines were designed to form the cone and cylinder shape, respectively. Further, two methods were adopted to link the two forming pass sets and spin the cone-cylinder combined shape. One is to connect the cone and cylinder forming lines directly (Schemes A); the other is to connect the cone and cylinder forming lines by transition lines (Schemes B). The effects of two key parameters (roller path and feed ratio f) on the wrinkling and wall thickness distribution were analyzed. The product exhibited wrinkling on the wall using the roller path of Scheme A with f = 0.5 mm/r. f affected the occurrence of wrinkling considerably. Larger f made the flatness of the cylinder wall worse, no matter which roller path (in Scheme A or B) was used. When f was set to 0.25 mm/r (f was lower than L-T1 in this study) with a blank thickness of 2.05 mm, wrinkling could be suppressed in the roller path of Scheme A. The product had an increasing thickness distribution on both the cone and the cylinder. The cylinder wall was even thicker than the disk blank with a blank thickness of 2.05 mm.