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With the growth of capacity of high voltage direct current (HVDC) transmission lines, the ratings of thyristor valves, which are one of the most critical equipments, are getting higher and higher. Verification of performance of thyristor valves particularly designed for HVDC project plays an important role in the handover of products between the manufacturer and the client . Conventional test facilities based on philosophy of direct test cannot meet the requirements for modern thyristor valves. New test facilities with high ratings are necessarily built based on philosophy of synthetic test. Over the conventional direct test circuit, the later is an economical and feasible solution with less financial investment and higher test capability. However, the equivalency between the synthetic test and the direct test should be analyzed technically in order to make sure that the condition of verification test in a synthetic test circuit should satisfy the actual operation condition of thyristor valves existing in a real HVDC project, just as in a direct test circuit. Equivalency analysis is focused in this paper, covering the scope of thyristor valves' steady state, and transient state. On the basis of the results achieved, a synthetic test circuit of 6500A/50kV for operational tests of thyristor valves used for up to ±800kV HVDC project has newly been set up and already put into service in xi'an high voltage apparatus research institute (XIHARI), China. Some of the results have been adopted also by a new national standard of China.