In order to study the effect of air-entraining agent on the frost resistance of marine concrete and its beam bending capacity, a total of 100 rapid freeze-thaw tests were carried out on six marine concrete beams of two mix ratios and the corresponding freeze-damaged test blocks. The mass loss rate, the dynamic elastic modulus damage degree and the compressive strength loss rate were used to efficiently evaluate the degree of freeze-thaw damage of concrete. The degradation of the compressive strength of concrete as well as the changes in the coefficients of the equivalent rectangular stress diagrams were considered, and the formula for calculating the bending capacity of normal cross-section of marine concrete beams under freeze-thaw action was proposed. The results show that the addition of air-entraining agent can enhance the frost resistance of marine concrete and slow down the degradation rate of the cracking moment of beams, but the concrete strength and the ultimate moment of beams will be reduced. The proposed model can predict the bending capacity of the cross-section of marine concrete beams under freeze-thaw action better within 150 freeze-thaw cycles.