A direct conversion receiver and a DC offset cancellation method are provided. An RF module receives a transmission signal to generate an RF signal. A mixer converts the RF signal to a mixer output comprising baseband and imaginary parts. A filter module filters out the imaginary part of the mixer output and adjusts gain of the baseband part to generate a baseband signal. A calibrator performs a calibration to determine a mismatch value of the mixer. A static DC offset canceller provides a constant offset compensation according to the mismatch value; wherein the mismatch value is used to minimize component mismatching effects of the mixer.