Modern power thyristor valves have a high power rating and are difficult to be tested in a conventional back-to-back test circuit. A more economical alternative is to use a synthetic circuit. The core to design a synthetic test circuit is to correctly reproduce the stresses applied on the thyristor valves. A new synthetic test circuit is introduced in this paper. This new circuit reproduces the correct stresses applied on the high voltage direct current（HVDC）thyristor valves in service. Verifying tests reveal that the circuit design is a success.