Abstract: Because of the existence of AC-DC combined electric field in converter transformer, whether the convention DGA method can be used in converter transformer still remains unclear.So a set of platform for dissolved gas in oil analysis of column-plate discharge was built to compare the difference in DGA between AC and AC-DC combined voltages. The test results show that the dissolved gases characteristics for oil-paper insulation with different voltage types under column-plate electrode are different, which means that fault can be detected earlier when gas contents and gas-produced rate are bigger, and the change of generated gas in earlier stage under composite AC and DC voltage level is not obvious and there is no insulation effect after the sudden increasing of generated gas during final phase. In addition, the diagnosis results of DGA for oil-paper insulation fault with different voltage types under column-plate electrode are same, which means that the DGA diagnosis standard has certain applicability in converter transformer.