"Tomorrow is his birthday" 这句话的英文表达就是 "Tomorrow is his birthday"。
这句话的意思是明天是他的生日。其中，"tomorrow" 是 "明天" 的意思，"is" 是助动词，"his" 是所有格代词，"birthday" 是 "生日" 的意思。
例句:
"Tomorrow is John's birthday, we should get him a present."
(明天是John的生日，我们应该给他买礼物。)
"I can't wait for tomorrow, it's my sister's birthday."
(我迫不及待地等明天，那是我姐姐的生日。)
"Don't forget, tomorrow is our boss's birthday."
(不要忘记，明天是我们老板的生日。)