The invention provides a method for predicting and evaluating concrete strength deterioration under an ocean environment. The method comprises the steps of detecting data of strength deterioration of concretes in different ratios under the ocean environment along with age through experiments; dividing the obtained operating data into a training group and a testing group, wherein factors which influence the concrete strength are used as a factor attribute set, and a strength deterioration state is used as a deterioration result attribute set; modeling a decision-making tree: selecting an output branch according to an attribute value of a corresponding attribute until a leaf node is reached, andoutputting an operating category for storing the leaf node as an analysis result; evaluating a model performance; and cutting branches of the established decision-making tree by use of a C4.5 algorithm. For complex concrete service environment deterioration conditions and final deterioration state responses, a final decision-making tree diagram is obtained by use of an ID3 algorithm, branches of the decision-making tree are reduced by use of the C4.5 optimization algorithm, the performance of the decision-making tree can be obviously improved, the concrete strength deterioration state under the ocean service condition is predicted and evaluated, an instant message of building strength deterioration can be obtained, and the risk caused by damage to building durability is assessed in advance.