The research is execute on the example of the main gate of the upper head of the locks No. 25-26 of the Saratov Hydraulic project of the Federal State-Funded Institution «Administration of the Volga Basin». Follows from results of earlier executed researches that the main destructive processes of aging reducing technical condition of gate and locks of navigable hydraulic engineering constructions are corrosion and corrosion and fatigue damages of their elements which realization is establish on separate elements of the studied metalwork. Use as the diagnostic parameter of size of corrosion wear of elements at high degree of roughness of their surface because of impossibility of his measurement with a necessary accuracy and lack of correlation at this operational phase of a metal construction with process of corrosion and fatigue process of the damage defining actual state of gate is incorrect. In process, growth of size corrosion wear elements the deflection gate which is the integrated indicator characterizing their elastic deformation will increase. The provide value of the allowed deflection of lifting and lowering gate under a pressure can't be considered now as the indicator correlating with change of a condition of their elements in time. The possibility of use of the provide value of an admissible deflection of gate as the diagnostic parameter of their technical condition is considered. Analytical evaluation of change of size of a deflection of lifting-gate from a hydrostatic pressure at various values of corrosion wear of their elements is execute. The discrepancy of the standard allowed values of a deflection of the lower girder of gate to the size of corrosion damage of their power elements is established. The field of possible realization of process of corrosion fatigue damage of power elements of the considered metalwork is define. The results presented in work can be used for correction of the established criteria values of indicators of safety for the considered metalwork of gate. The stated technique of check of a possibility of use of an indicator of a deflection of the lower crossbar of lifting-gate under a pressure as the diagnostic parameter of their technical condition can be used when checking efficiency of other diagnostic indicators of elements regulated by the specifications and technical documentation of the mechanical equipment of navigable hydraulic engineering constructions both operated, and designed.