There are ibus and fcitx almost people used for chinese pinyin input method.

1. ibus which I think more quick introduced first
   You can avoid install ibus if there has been installed on ubuntu
   sudo apt-get install ibus ibus-clutter ibus-gtk ibus-gtk3 ibus-qt4
   change to ibus input program
   im-config -s ibus
   install google pinyin
   sudo apt-get install ibus-pinyin
   Restart the computer and conduct the below command
   sudo ibus-setup
   setup window will occurs, then add the chinese-pinyin will be ok