In the actual service environment, the low alloy and high strength structural steel will be affected by the cyclic alternating load and corrosion damage caused by the corrosive medium, so that the service time of structural steel will be significantly shortened. The work aims to study the fatigue strength and fracture mechanism of ASTM A572 Gr65 low alloy high strength structural steel under different environments. According to the standard, ASTM A572 Gr65 structural steel was made into standard samples with a length of 52 mm. Rotary bending fatigue tests were carried out on QBWP-6000 rotary bending fatigue test machine under the environment of laboratory, deionized water and 3.5% NaCl solution, and the loading frequency was 100 Hz. The fixed stress ratio of the rotary bending fatigue testing machine was R=?1. When the sample failure or loading times reached 107 times, the test was stopped and the fatigue test value was recorded. In origin software, the experimental values under different strength were fitted to obtain the fatigue strength under this environment, and the fatigue strength of structural steel under different environments was compared. The sample was cut with wire cutting and the cross section was polished, and corroded with 4% nitrate alcohol solution. The microstructure of the fracture was observed by metallography microscope (CX40M) and scanning electron microscope (ZEISS Gemini 300). The energy spectrum of each corrosion fatigue fracture was collected by energy spectrometer, and the components were analyzed. Then, the changes of microhardness values near the fracture were measured by microhardness tester (ZHVST-1000C) to explore the fatigue failure mechanism under different environments.