I want to use a travel router to increase connection of my raspberry pi AP. How can I use the USB travel router as wlan1. Then Use wlan1 as my AP interface.
"How can I use the USB travel router as wlan1"... IMHO, your question is far too vague to answer because it depends largely upon which travel router you use, and other specifics you have not included in your question.
I will say that you can use a travel router with your RPi, and will make these suggestions:
Select a specific travel router from one of the "usual sources", and read the documentation. FWIW, I like these OK.
Before you invest too much in this idea, perhaps give some thought to the "other issues" you may encounter in your anticipated use-case (traveling, I presume). For example: will batteries be required, Internet connectivity?, etc. I say this not to discourage, only to share my view that RPi may not be the best "traveling companion".