Three Gorges-Changzhou（3G） HVDC thyristor valves have a high power r at ing per thyristor level. Testing of these thyristor valves by using a convention al Back-to-Back test circuit would necessitate huge investments and would not gi ve an improved testing regime than produced by the solution chosen. A synthetic test circuit using the conventional Back-to-Back test circuit to supply the curr ent and an oscillating circuit to supply the voltage has been developed for the testing of the 3G thyristor valves. The conditions of the four operational state s of HVDC thyristor valves can be adequately represented in this synthetic test circuit. The test parameters used gave test stresses on the test object equal to or higher than those that are foreseen to appear in service. The successful typ e test results showed that the design of 3G HVDC thyristor valves is fully adequ ate. The tested modules have also shown a substantial margin in the thyristor va lve design since

for most of the tests

the test parameters were globally more severe than specified.