An extraction method is proposed for the equivalent circuit parameters of an X-band PIN diode based on waveguide measurement. For the S-parameter measurement, a network analyzer, a waveguide, a transition, two identical adapters, and a 1×2 unit cell with two PIN diodes were used, and the equivalent circuit parameters of the PIN diode were extracted from the measurement results. The thru, reflect, line calibration method was adopted to reduce undesired errors in the components used for measurement, and the equivalent circuit parameters of the PIN diode were determined from the measurement results, where the effect of adapters was corrected.