The rolling of inside right-angle step has always been one of the key technologies of cross wedge rolling(CWR). The general formula and algorithm of rolling alignment curve are not suitable for the production of small right-angle steps. In order to solve this problem, by improving the geometric model, a new calculation method is proposed for the volume of spiral cone of the small right-angle step. According to the characteristics of the cross wedge rolling process, by comparing the initial radius of rolled product and the corresponding auxiliary circle radius,the preliminary judgment conditions for the small inside right-angle step was pointed out. According to the relationship between the radius of large section and the rotation angle, the shaping process is divided into three phases. The volume formula of each phases is deduced by dividing the spiral cone into three regular volumes. Based on the volume fixedness theory, the accurate shaping curve of the small right-angle step with the change of the rolled piece rotation angle is obtained. Finally, the finite element software Deform-3D is used to simulate the large diameter part within a certain area reductions range, which verifies the applicability of the calculation method proposed in this paper. At the same time, through comparative analysis, it is found that the stretching angle should be as small as possible when forming large diameter shaft parts with small right-angle steps.