Abstract: In order to realize low-cost measurement of vector reflection coefficient, a vector reflection coefficient (one type of S parameter)measurement system is built with LimeSDR software radio module, directional coupler and GNU Radio Compainon software in this paper. In order to verify the accuracy of the system, the data of three calibration parts (open circuit, short circuit, load) are measured, combined with the actual parameters of the calibration parts measured by the vector network analyzer, and the error parameters of the microwave network are calculated. Then, a specially selected device (SSD) is measured and error correction is performed to obtain its vector reflection coefficient. Compared with the experimental results of measuring the same SSD with a vector network analyzer, the results show that the built measurement system has high measurement accuracy, and the system has the characteristics of low cost, flexible configuration and strong scalability.