The stress-strain state determination and the study its change as a result of plastic deformation development in the process of loading of the welded rotor of a complex shape has been carried out in the article. The choice of the calculation scheme is very important when considering such responsible objects. The calculation of the rotor as a single component, located in a axis symmetric elastic-plastic state, is quite complicated. Triangular elements of the linear law of displacement distribution, adopted as a basis in many works, allow more flexible than rectangular elements, to approximate the contour of any form. But the use of finite element of this type leads to an increase in the total number of unknowns. The stressed state of the rotor of the steam turbine K-1200-240-2 is of sufficient complexity and must be matched to the study as a spatial problem. An approximate estimation of stress distribution in similar structures can be made on the basis of calculation of separate parts of rotor. With other ratios of stiffness of discs and jumpers, this issue requires additional research. Despite the fact that maximum stresses are observed in the zones of rounding, the most stressed areas are points of the cross-section near the rotation axis. In general, the results obtained in this article show that the use of finite elements, based on the momentary finite element sheme equation and taking into account the variability of geometric parameters allows to calculate the rotor in a statement, which takes into account all the geometric features of the design without any simplifications.