The invention discloses a phase adjusting device for a split-body gear of a mechanical press, which comprises an adjusting block provided with a pin shaft and an adjusting bolt; a hub is provided with a gap and a gear ring is provided with a pin hole; the adjusting block is arranged in the gap and two sides of the adjusting block are provided with bolt perforations for locking the adjusting bolt;and the adjusting block is connected with the gear ring by inserting the adjusting bolt into the pin hole. The invention also provides a method for adjusting the phase of the split-body gear, and themethod comprises the following steps: 1) processing the pin hole for arranging the adjusting block, and processing the gap for arranging the adjusting block; 2) manufacturing the adjusting block and the adjusting bolt; 3) arranging the adjusting block in the gap, arranging the adjusting bolt at the two sides of the adjusting block, and adjusting the adjusting bolt to cling to the two surfaces of the gap on the hub; and 4) determining the phase difference of an integral gear and the split-body gear, and adjusting the adjusting bolt correspondingly according to the calculated result. The phase adjusting device has the advantages of comparatively simple structure, convenient manufacture and low cost. The phase adjusting method only needs 0.5 hour.