The present disclosure belongs to the technical field of preparation of functional materials, and in particular relates to a grinding aid for cement and a preparation method therefor. The components of the grinding aid include a modified alcohol amine of a specific structure and a polycarboxylic acid polymer of a specific structure, and a mass ratio of the modified alcohol amine to the polycarboxylic acid polymer is (1-10):(40-49), and the early strength of the cement can be increased, the water consumption can be reduced, and the fluidity can be improved when the grinding aid is used in cement. The present disclosure adopts the combined action of the modified alcohol amine and the polycarboxylic acid polymer in specific ratios and structures, so that a synergistic effect can be achieved, and the respective performance advantages can be fully exerted.