The invention discloses a modified Mannich amide polycondensate cement grinding aid, and a preparation method and application thereof. The preparation method for the cement grinding aid comprises thefollowing steps: uniformly mixing a phenol monomer, formaldehyde and a polyamine monomer, and performing a polycondensation reaction at 100 to 150 DEG C to obtain a Mannich amide polycondensate; and then subjecting the Mannich amide polycondensate and epoxy monomers to an addition reaction to prepare the modified Mannich amide polycondensate cement grinding aid. The cement grinding aid of the invention is produced by using a one-pot method; no waste is produced; the preparation method is simple in process and favorable for large-scale production; the produced cement grinding aid has low dosagewhen applied to cement grinding, shows good grinding effect, and can greatly save the cost of cement manufacturers; and the cement grinding aid has good adaptability to mixed cement materials, can effectively optimize cement grain grading, and significantly improves the early and late strength of cement.