Modern power thyristor valves have a high power rating and are difficult to test in a back-to-back test circuit in the test laboratory.Verification of thyristor valve design with synthetic test circuits is an alternative.The core to design a synthetic test circuit is to correctly reproduce the stresses applied on the thyristor valves.Voltage and current stresses on the thyristors under four operational states are highlighted in this paper.A new synthetic test circuit has been developed by ABB Power Systems.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 was a success.