The invention provides an MMC (multi-media card)-HVDC (high-voltage direct-current transmission) sub-module bypass switch testing device. The device comprises an interface module, a master control module, a display module and a power module, wherein the interface module is connected with a bypass switch; the master control module is used for detecting action time of the bypass switch; the display module is used for judging whether the action time of the bypass switch is qualified or not; and the power module is used for supplying power for the interface module, the master control module and the display module. By the MMC-HVDC sub-module bypass switch testing device, the action time comprising closing time, bounce time and return time of the bypass switch can be accurately and quickly detected, and whether the bypass switch meets requirements of the MMC-HVDC sub-module or not can be judged.