Signal processing system and signal processing method cooperating with variable gain amplifier

The invention provides a signal processing system, which comprises a variable gain amplifier, an analog-to-digital converter, a gain compensation module and a signal processing module. The variable gain amplifier applies a variable gain to an analog input signal to generate an amplified analog signal. The analog-to-digital converter converts the amplified analog signal to an amplified digital signal. The gain compensation module applies a compensation gain to the amplified digital signal to generate a compensated signal. The gain compensation module allows the variable gain and the compensation gain to keep an added gain of the amplified digital signal to have an instantaneous variable quantity lower than a predetermined threshold value. The signal processing module performs a signal processing procedure on the compensated signal.