A reasonable and applicable chloride ion diffusion model for fatigue damaged concrete structures exposed to seawater freeze–thaw environments was proposed, And the service life of reinforced concrete beams with fatigue load levels of 0.2 and 0.3, fatigue loading times of 200,000–400,000 under seawater immersion alternating freeze–thaw cycle environment were predicted. Results show that the expected service life of concrete beams without fatigue damage under seawater immersion alternating freeze–thaw cycle was 6.0 years, respectively, which was far less than the requirements of existing specifications for the service life of concrete structures. The service life of concrete structures further decreased as the fatigue load increased. For concrete beams with a fatigue load level of 0.3 loaded 400,000 times, under the alternating freeze–thaw cycles of seawater immersion, the expected service life is only one year.