Abstract: Compared with Short-Open-Load-Thru (SOLT) calibration, Thru-Reflect-Line (TRL) calibration is a more accurate and easy-to-implement calibration method, especially suitable for non-coaxial measurements with more than two ports and multiple ports. In this paper, aiming at the S parameter measurement problem for Wolfspeed′ s GaN transistor CGH40010F, the error box model in a network analyzer for the TRL calibration kit is analyzed. On this basis, a set of TRL calibration kits is designed and manufactured. The operation frequency range is 1-6 GHz. The amplitude of Sii(i = 1,2) is less than -15 dB and the amplitude of Sij(i,j = 1,2;i≠j) is greater than -0. 8 dB for both of the thru and the delay-line standard components in this frequency band. The calibration parameters are set into the vector network analyzer for calibration test. The actual measurement results illustrate that the small signal S parameters of the GaN transistor after TRL calibration are consistent with the results in the official data manual, verifying the validity of the calibration measurement method and the TRL calibration parts designed and manufactured according to it.