The invention provides a method and a device for determining an echelon utilization battery energy storage system consistency maintenance index. The method and the device relate to the technical field of echelon utilization batteries. The method comprises the steps of: sampling to obtain a battery module to be tested, conducting multiple charge and discharge tests on the battery module to be tested according to preset operating conditions for tests, and recording operating parameters; determining surplus capability of the battery module to be tested after conducting every preset number of charge and discharge tests, determining indexes of each single battery in the battery module to be tested according to the operating parameters, and determining ranges, mean square deviations and dispersion parameters the indexes of the battery module to be tested; determining correlation coefficients of the surplus capability of the battery module and the index ranges to be tested, correlation coefficients of the surplus capability of the battery module to be tested and the index mean square deviations, or correlation coefficients of the surplus capability of the battery module to be tested and the index dispersion; and determining a consistency maintenance index of the battery module to be tested according to the correlation coefficients.