Under long-term loading, the deformation of reinforced concrete flexural members is an important index and it is one of the checking contents of the serviceability limit state. To study the degradation law of bending stiffness of marine high performance concrete beams after action of repeated loads, total 10 test beams were designed and fabricated. After exposure to the repeated load test, the chloride solution dry-wet cycle test and their coupled test, the mid-span deflection development and stiffness degradation of test beams were evaluated using the four-point bending test. A modified method for the code formula of beam short-term stiffness is proposed. The test results indicate that when the load level is determined according to the moment of the beam’s pure bending section equal to 0.4Mu, the damage degree in concrete approaches 15% after 30 cycles of repeated load. For the test beams only exposed to the chloride solution dry-wet cycles, their mid-span deflection develops slower than that of the reference beam. After the action of repeated loads, the mid-span deflection of these test beams develops faster than that of the reference beam. When the damaged beams were exposed to chloride solution dry-wet cycles, their degradation of bending stiffness becomes more obvious. Based on the experimental results, the damage effect reduction factors were proposed to revise the calculation formula of beam’s short-term stiffness. The rationality and effectiveness of the revised formula are verified by the test data.