The invention discloses a method for evaluating auxiliary service efficiency of an automatic generation control (AGC) set. The method comprises the following steps of utilizing actual output of the set and correlation of an area control error (ACE) sequence of a power grid as effectiveness indexes for set adjustment in each fixed calculation period; calculating to obtain an actual frequency modulation range and instruction complete rate according to the actual output and target output of the set in each fixed period, calculating to obtain frequency modulation multiplied range by considering an actual adjustment range of the set, and comprehensively taking each subitem index as a contribution index of the set; and respectively calculating an expected adjustment target and an adjustment rate influence factor of the set in each fixed period, and taking a product of the adjustment rate influence rate and the minimum value between the two targets as an adjustment accuracy index of the set. Each independent performance index is comprehensively evaluated and analyzed, and the auxiliary service efficiency of the AGC set is more thoroughly, accurately and reasonably evaluated.