Internet is widely available through out China, but there are some things to note:
some sites are blocked or restricted, such as YouTube, Facebook, Twitter
most internet cafes won't allow foreigners to use, unless they have a Chinese ID card
The good news is that wi-fi is widely available in hotels and cafes, often free, but password protected.
If you need to access blocked sites, including some blog sites, consider getting VPN (proxy server). There are some free ones you have to download from before you reach China, or some sites you can try while in China.