come on in 的意思是"進來吧".當有人敲門的時候你允許別人進入你的房間的時候你可以說"Come on in, please."(美國人常說)
come on in 相當於Please come in請進來。又如： Come on in and have a chat.請進來聊聊吧。 If you 're thinking of becoming a journalist like me, I'd be the last to dicourage you. Come on in, the water's fine!如果你想像我一樣做一個新聞工作者，那我決不會勸阻你。來吧，快來吧！
Come on in比come in 帶有更多的誘勸的'意味。也作come down，come on out, come on round, come on up等。第二個例子中的come on in, the water's fine!原來是親人跳入河海等中去洗澡的意思。
