The invention discloses a digital automatic gain control method and system. The method comprises the steps of firstly, sampling and averaging a digital output signal of a analog-to-digital converter in a receiver, to acquire an average value of the current receiver digital output signal; 2, putting the value into multiple comparators to be compared with multiple reference values, wherein 0 or 1 output by each comparator is a comparison result of the bit, and the overall comparison results of all the comparators are formed into a vector; 3, putting the vector into a gain look-up table as an address, and outputting stepping, needing to be adjusted, of gain iteration by the look-up table; and 4, overlapping a current gain control word and the stepping output by the look-up table to gain a newgain control word, thus achieving automatic gain control on a variable gain module. According to the method and system provided by the invention, the circuit power consumption and area are saved under the premise of ensuring that the system convergence time is relatively stable.