His eyes were overflowing with pride when he showed his artwork.

overflowing 是动词 overflow 的现在分词形式。overflow 由前缀 over-（表示"超过"）和动词 flow（流动）组成，字面意思是"流出来"，引申为"充满、洋溢"。 overflowing with... 这个短语表示"充满...的"，常用来形容情感满溢的状态。