We may consider to upgrade the router to 7x00 model for furture expension. below two models I prefer.
what is the main diffrerent of them? any link or doc about it?
The main difference between the two, the 7301 is a complete compact router, the 7200-NPE-G1 is one of the "engines" that can be used within the 7200VXR chassis. Both should be about the same with regard to performance or IOS features (excluding using certain hardware non-interface service modules or PAs). Price wise, I would expect the 7301 to cost less. Feature expansion, the 7301 only has one PA slot, the 7200VXR chassis two models offer many more slots for various cards including the engine which could be upgraded to the 7200-NPE-G2 (NB: 7201 is the compact version).
The product pages provide even more information:
Below is a URL that has some good comparison between those two platforms.
Cisco 7200 and 7301 Series Routers
*Pls rate if it helps*