The invention provides a representation method for describing an old fault top surface structure diagram. The representation method for describing the old fault top surface structure diagram comprises the steps that 1, the top surface of an eroded and lifted stratum is interpreted according to logging information of a drilled well; 2, fault interpretation is performed in a seismic section, and fault combination is performed on a plane after the interpretation on the seismic section is completed; 3, fault classification is performed according to the fault displacement existing situations of faults on a top interface, and fault grading is conducted on the faults according to the fault displacement amounts and the lengths of the faults. By means of the representation method for describing the old fault top surface structure diagram, the problem of representation of blind faults on the top surface structure diagram is effectively solved. The representation method has the great significance on oil-gas exploration work of a front tertiary stratum, is simple, clear and good in operability and has very good practicability in structure diagram drawing.