The present invention discloses a background calibration system and method for calibrating the non-linear distortion of the amplifier. The calibration method in the present invention includes: generating random sequences and inputting the random sequences in different amount and different sets into an amplifier; amplifying the random sequences and detecting linear and non-linear coefficients; quantizing the output linear signal from the amplifier, and generating a digital output signal; multiplying the digital output signal to generate a high-order signal; generating an estimated non-linear error for the amplifier by multiplying the high-order signal with the estimated non-linear coefficient; adding the non-linear signal with the digital output signal to generate a linear output signal; calculating the random value from the parameter extractor to determine the occurrence of non-linear distortion in the circuit, and further adjusting the non-linear coefficient to calibrating the amplifier.