The paper describes a W-band six-port reflectometer, including its design, calibration and error analysis. The waveguide junction is designed optimally by the use of the concept of generalized resonant cavity. The diode detectors are used as powermeters which are matched well. The equipment has been calibrated by many methods. For meas- uring two-port network parameters, a least square method is proposed, which has merits of easiness, quickness and high accuracy.