"He couldn't help but laugh" 这句话的意思是：他禁不住笑了。
这句话的来源是英语中的固定搭配。其中的 "couldn't help but" 意思是禁不住，"laugh" 意思是笑。
例句：
He couldn't help but laugh when he saw the funny video. (他看到那个搞笑的视频时，禁不住笑了。)
She couldn't help but smile when she heard the good news. (她听到好消息时，禁不住微笑。)
I couldn't help but cry when I saw the sad movie. (我看到那部悲伤的电影时，禁不住哭了。)