The invention provides a digital AGC control method and system based on FPGA. The method comprises the following steps: receiving a sampling signal obtained by sampling an output signal of an AGC chipby an analog-to-digital converter; computing a power value of the sampling point, and performing detection processing on the sampling signal after the power value computation according to a preset detection condition; if judging that the sampling signal power value difference between any two adjacent computations in the first preset time quantum is not bigger than a first preset threshold, determining a standard power value based on the sampling signal power values computed in the first preset time quantum; and if the standard power value exceeds a preset sampling interval of the analog-to-digital converter, configuring a gain value of the AGC chip according to the standard power value and an interval value of the analog-to-digital converter preset sampling interval, thereby enabling thesampling signal power value sampled by the analog-to-digital converter to be located in the preset sampling interval. The control method provided by the application has the features of being fast in convergence time and large in dynamic range, and provides guarantee for accurately estimating the signal amplitude in the private network monitoring.