A system for correcting a DC offset includes a digital-to-analog (D/A) converter module (30), a summing circuit (40), an inphase-to-quadrature (I/Q) modulator (50), a spectrum analyzer module (60) and a DC offset correction module (70). The D/A converter module converts digital control signals to analog control signals, and outputs DC offset regulating signals. The summing circuit respectively sums up the DC offset regulating signals and corresponding vectors of a base band signal. The I/Q modulator receives the summed base band signal, and converts the summed base band signal to a radio frequency (RF) signal. The spectrum analyzer module analyzes an energy variation according to a DC offset contained in the RF signal. The DC offset correction module outputs the digital control signals to adjust the DC offset regulating signals, thereby obtaining the lowest energy variation.