In order to test the S-parameters of non-coaxial RF (Radio Frequency) devices accurately, using ADS (Advanced Design System) to simulate and design a set of fixture and calibration pieces for noncoaxial RF device performance test, and the calibration pieces is used to calibrate the test fixture, remove the error introduced by the fixture, and obtain the real S parameters of non-coaxial RF microwave devices. Based on the study of various parameters of RF microwave devices, the Engen's TRL (Thru-Reflect-Line) calibration algorithm is studied in depth. An improved TRL calibration algorithm is proposed. And the use of MATLAB program to achieve two calibration algorithms to correct the system error introduced by the measuring fixture, so as to get the real performance parameters of the device under test. Through the test of the verification device, the agreement between the improved TRL algorithm and Engen's TRL algorithm is verified. The final design of the test fixture can be successfully applied to the network analyzer for noncoaxial RF devices S-parameter measurement.