This paper discusses the monitoring of the fatigue life of a steel bridge through the statistical analysis of strain-time data collected by a structural health monitoring system that is permanently installed on the bridge being studied. The Rainflow counting method was used for the statistical analysis of the strain monitoring data under vehicle load, where the dependence of the stress range on the number of cycles was determined. First, the time-frequency characteristics of the short-term strain monitoring data from the steel bridge in the Czech Republic were analyzed. A stress recording unit with an oscillation counter was used for long-term continuous monitoring of the time-varying signals, including their digitization, evaluation by the Rainflow method and recording of the number of cycles divided into classes according to amplitude magnitudes. Additionally, the time history of temperature measured by the built-in temperature sensor was also recorded. This system enables long-term recording and evaluation of data from various types of sensors and physical transducers. The analysis of the recorded data and the results obtained were used to verify of the long-term loading and assess the fatigue life of the structure.