The invention discloses a device and a method for detecting polarities of current transformers of an alternating current filter group. The device comprises a signal acquisition unit and a quantity adding detection unit. The signal acquisition unit is connected with current transformers on the head end and the tail end of a to-be-detected alternating current filter group. One end of the output end of the quantity adding detection unit is accessed to an inner side lead of the photoelectric type current transformer on the head end of the to-be-detected alternating current filter group, and the other end is accessed to an inner side lead of the photoelectric type current transformer on the tail end of the to-be-detected alternating current filter group. The method comprises a step of judging polarities of the current transformers on the head end and the tail end of the alternating current filter group based on acquisition signals of the signal acquisition unit. According to the invention, polarities of whole sampling channels (including a body, a secondary signal transmission channel, a combination unit and a protection device) of the current transformers on the head end and the tail end of the alternating current filter group simultaneously, so workload of polarity detection can be greatly reduced and the device and the method are advantageous in that the device and the method are easy to implement and vivid.