come on in 的意思是"进来吧".当有人敲门的时候你允许别人进入你的房间的时候你可以说"Come on in, please."(美国人常说)
come on in 相当于Please come in请进来。又如： Come on in and have a chat.请进来聊聊吧。 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!如果你想像我一样做一个新闻工作者，那我决不会劝阻你。来吧，快来吧！
Come on in比come in 带有更多的诱劝的'意味。也作come down，come on out, come on round, come on up等。第二个例子中的come on in, the water's fine!原来是亲人跳入河海等中去洗澡的意思。
