Considering the hidden danger caused by large grid-connection deviation for half-wavelength AC transmission systems, difficulty to simultaneous adjustment of grid-connection parameters at both ends of half-wavelength line due to its long distance, and future variety of grid-connection structures for half-wavelength systems, this paper designs three typical kinds of grid-connection structures of half-wavelength transmission line and uses the flexible device for grid-connection adjustment. Then, the equivalent circuit of half-wavelength transmission system connected with UPFC is analyzed, and also the applicability of the flexible grid-connection device is studied. By simulating in Matlab/Simulink platform, the results show that the flexible grid-connection device is suitable for multi-structure half-wavelength transmission lines, and it can generally improve the grid-connection characteristics. The results can provide support for multi-structure grid-connection control of half-wavelength transmission projects in the future. This work is supported by National Natural Science Foundation of China (No. 51477098) and Science and Technology Project of State Grid Corporation of China (No. SGXJDK00DJJS1600151).