This paper discusses the application of the fiber-optic technologies in measuring the parameters of the stress-strain state of a seamless track rail. Measuring modules are attached directly to the side surface of the rail and contain fiber-optic sensors with a special structure for changing the refractive index along the length of the base part. The values of deformations are determined during full-scale measurements when analyzing changes in the parameters of the light pulses passing through an optical channel with Bragg gratings. The implemented approaches in measurements and simulation are relevant for the sections of the railway track that are most susceptible to deformations with a large gradient of values, for example, at turnouts, in the places of subgrade heaving, etc.