When forecasting the technical state of the parts and units of railway rolling stock in operation, an important task is to determine the shape of the discontinuity in ultrasonic non-destructive testing in order to predict its behavior in further operation (this is especially important if the discontinuity in the results of such control is acceptable). Author proposed a solution for the improvement of the two-frequency defectometry method. A mathematical apparatus was developed and a method for determining the coefficient of the discontinuity shape was elaborate on its basis. The method makes it possible to determine the shape of both a point and an extended discontinuity. The software product NDTRT-07.03.01.18 was developed to automate calculations in determining the shape of discontinuity by a two-frequency method. The article gives a description of the experimental studies carried out to evaluate the reliability of the proposed method. This method can be used in determining the shape of the discontinuity in the details of the rolling stock, in which the defect can have a different shape, for example: cast wheel centers; various shaped castings used in the manufacture of rolling stock units (brackets for locomotive bogies, cast sidewalls for cars), as well as in parts manufactured by the method of plastic deformation, including wheel treads, axles, all-rolled wheels, rolled wheel centers, etc. In these details discontinuities are predominantly planar in nature, but voluminous discontinuities are also encountered - non-deformable nonmetallic inclusions, therefore the developed method can be applied to such objects of rolling stock railways.