The invention discloses a processing method for converter trunnion deep-hole which includes dismantling a rotation joint assembly at a trunnion end portion to clean the end face of the trunnion; marking the position of the deep-hole to be processed at the end face and installing a casting blank foundation member in a processing area; placing a mechanical slide unit on the casting blank foundation member, installing a milling power head at the mechanical slide unit and assembling a deep-hole drill at a main shaft of the milling power head; adjusting the height of the mechanical slide unit and the feed straightness of the deep-hole drill according to the marked position; fixing the mechanical slide unit at the casting blank foundation member; and processing the deep-hole to be processed by using the milling power head arranged at the mechanical slide unit. The processing method can perform deep-hole processing on the converter at a production line. The invention also discloses a processing device for converter trunnion deep-hole. The processing device comprises the casting blank foundation member, the mechanical slide unit fixed on the casting blank foundation member, the milling power head assembled at the mechanical slide unit and the drill assembled at the milling power head.