He dammed up his anger and didn't lose his temper on the spot.

dammed 是动词 dam 的过去式。dam 本义是"筑坝拦水"，在这里用作比喻，表示"抑制、控制（情绪）"。 damm up 这个短语用筑坝拦水的意象来比喻"压抑、抑制（情绪）"，就像用堤坝拦住水流一样控制住愤怒。