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In the die-less spinning of the conical part, the forming state changes during the spinning process and depends on the forming parameters, which has a critical effect on the forming quality of the spun part. In this paper, a criterion of the forming states is established, and its dependence on the forming parameters is investigated. It is found that the formed wall thickness changes during die-less spinning. According to the formed wall thickness variation degree, three forming states are defined: shear spinning state ( t f = t 0 s i n α , where t 0 and t f are the initial and formed wall thicknesses, respectively, and α is half-cone angel), the conventional spinning state ( t f > 0.9 t 0 ), and transition state between the shear and conventional spinning states ( t 0 s i n α < t f ≤ 0.9 t 0 ). The distribution of stress and strain in three forming states is obviously different. The die-less spinning always proceeds in the sequence of shear spinning state, transition state, and conventional spinning state. The initial forming state may be any one of them, which is mainly determined by the diameters of the blank and general mandrel. Thus, the quantitative dependence of initial forming state on the diameters of blank and general mandrel is further analyzed, and a criterion for the initial forming state is correspondingly established. In addition, the influence of forming parameters, including the blank parameters, mold parameters, and process parameters, on the criterion for the initial forming state in die-less spinning is revealed. This paper could improve the understanding of the deformation mechanism in die-less spinning. [ABSTRACT FROM AUTHOR]