The invention discloses a method of determining a storage-battery lagging single battery based on an internal resistance entropy value method. The method comprises the following steps that firstly, a measured storage battery is formed by m single batteries, an internal resistance value of each single battery is measured at intervals of a period of time and the measurement is performed continuously for n times; the m single batteries are numbered by j and i is equal to 1, 2, ...m; the times of measurement of each single battery is numbered by the i, wherein i is equal to 1, 2, ...n; a proportion of the internal resistance value rij of a jth single battery during ith measurement in an internal resistance value sum of all the m single batteries after n measurements is calculated; then, according to the proportion, an entropy value of the internal resistance value of the jth single battery is calculated; and then, according to the entropy value, a difference coefficient of the internal resistance value of the jth single battery is calculated and the difference coefficients are ranked from large to small so that a lagging battery can be found out. The method has the advantages that a calculated amount is small; the method is simple and practical, and rapid and accurate.