A W-band sub-harmonic mixer was presented employing microstrip hybrid microwave integrated circuit. The parasitic parameter introduced by package structure of the diode was analyzed. Then a method is proposed to reduce the parasitic capacitance of the diode. In order to avoid grounding with via-hole and usage of edge-coupled band-pass filter in the W-band which are commonly encountered in traditional sub-harmonic mixers, a modified configuration of sub-harmonic mixer was proposed. The measured minimum single side conversion loss is 8 dB at a LO of 45 GHz and an IF of 2.4 GHz. The conversion loss is less than 10.5 dB in the range of 90~100 GHz.