A video signal processing system with a dynamic calibration loop of an ADC comprises a calibration switch for transmitting signals according to a control signal; a reference switch module for transmitting reference voltages according to a plurality of control signals; a reference voltage generator coupled to the reference switch module for providing the reference voltages; a coarse tuner coupled to the calibration switch and the reference switch module for coarse-tuning received signals; an ADC coupled to the coarse tuner for converting analog signals to digital signals; a fine-tuner coupled to the ADC for fine-tuning received signals; and a calibration logic module for controlling the calibration switch, the reference switch module, the coarse tuner, the ADC, and the fine tuner according to signals outputted from the fine tuner, so as to compensate errors of the ADC.