The proposed research is devoted to improving the acoustic diagnostic technique for the stress–strain state of metal structures’ shaped profiles. This is carried out using the echo reflection-shadow method of sounding sections of shaped profiles and transducers along their axis. The research develops a methodology for determining the acoustoelastic coupling coefficients for the material of shaped profiles, using the shelf and neutral line sections based on the difference method. The shelf section and neutral line correspond to the stressed and unstressed states of the metal, respectively. The research proposes a scheme for constructing a system for diagnosing the stress–strain state of metal structures’ shaped profiles, analyses it, and justifies the choice of technical means for its implementation. Software for processing and analyzing the results of diagnostics of the strain–stress state of metal structures’ shaped profiles has been developed. An analysis of the influence of the components of the total error on the result of diagnosing the actual mechanical stresses is carried out, and ways to reduce it are substantiated by developing a block of piezoelectric transducers and adjusting the measured time values depending on the ambient temperature. The ultrasonic wave transmission time intervals on the neutral line of shaped profiles are analyzed. The acoustoelastic coupling coefficients for metal structures’ shaped profiles for tensile and compressive stresses are determined. The improved acoustic method is proved to be possible in industrial conditions. A comprehensive methodology for diagnosing the stress–strain state of shaped profiles is proposed, which was used to perform acoustic diagnostics of the stress–strain state of metal structures’ shaped profiles of industrial buildings.