The invention belongs to the technical field of mineral monomer liberation measurement, in particular to an iron ore dressing product mineral monomer liberation measuring method, which comprises the following detection steps: screening and elutriating dressing products by granularity level, recording granular weight, testing the all-iron grades of the dressing products of all granularity levels, observing dressing products of all granularity levels under a microscope, dividing the dressing products by the area ratio of iron minerals to grain into monomer iron minerals, 7/8 iron minerals, 3/4 iron minerals, 1/2 iron minerals, 1/4 iron minerals, 1/8 iron minerals, 1/16 iron minerals, 1/32 iron minerals and monomer gangue minerals, counting the numbers of the mineral grains of all area sections of dressing products of all granularity levels, obtaining an original record of liberation measurement, inputting the weights of all granularity levels, all-iron grades and original data on libration measurement into an original data input interface of iron mineral dressing product libration computing software, computing the theoretical libration values of all granularity levels by using a formula and correcting the actually measured libration J(D) of all granularity levels. The method provided by the invention can process a large amount of libration measurement data quickly, effectively and more accurately.