Flexible fixtures increasingly acquire an extension in up-to-date manufacturing engineering, albeit an attempt to determine the impact of the flexibility on the fixture accuracy parameters was not performed in previous research. The aim of this work is determination the opportunity to provide dimension accuracy for lever machining in the high-flexible fixture. Experimental values of displacements of the elements of the system "fixture-workpiece" for the different levels of fixture flexibility were obtained by means of finite elements analysis. On the example of levers machining it was stated that increasing the fixture flexibility allows receiving in a certain range the required dimension accuracy of the parts. Displacements were used for obtaining the mathematical model of the fixture accuracy depending on fixture flexibility. This model in case of levers machining describes by nonlinear function of evaluated flexibility indicators. The method of quasilinear evaluation of the parameters was used for identification the design flexibility by minimization of the total square deviation using the iteration procedure.