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• Test method with hot-wet environments and random loads coupling action was proposed. • Fatigue failure mechanism of strengthened beams under coupling action was discussed. • Environmental random fatigue equations were established. Fatigue behavior of main load-bearing reinforced concrete (RC) members of highway bridges is heavily influenced by service environmental attacks and vehicle random loads. To investigate the fatigue behavior of RC beams strengthened with CFRP on highway bridges served under hot-wet environments and vehicle random loads, a novel environmental fatigue test method was proposed in the current research. Three-point bending fatigue tests on RC beams strengthened by carbon fiber laminate (CFL) with five combinations of hot-wet environments (10 °C & 50%R∙H, 23 °C & 78%R∙H, 50 °C & 50%R∙H, 50 °C & 78%R∙H, 50 °C & 95%R∙H) and three sets of random loading levels (ΔP mean = 18.3 kN, 19.9 kN, 21.6 kN) were carried out. The results showed that coupling action of hot-wet environment and vehicle random load has a significant effect on the fatigue failure mode (including tensile rebar fracture and CFL debonding), fatigue stiffness and fatigue lives of the strengthened beams. Fatigue lives of the strengthened beams under vehicle random loads was lower than constant amplitude loads and ladder amplitude loads. Environmental random fatigue lives decreased with the increase of relative humidity and temperature. To facilitate and accurate environmental random fatigue life prediction, environmental random fatigue equations which were able to consider the influence of coupling effect of hot-wet environments and the vehicle random loads on fatigue lives and fatigue limits of the strengthened beams were established and verified against the test data. [ABSTRACT FROM AUTHOR]