It's made up of 23 indicators, ranging from a nation's level of military expenditure to its relations with neighboring countries.
The data also comes from various sources, including the International Institute for Strategic Studies, the World Bank, various bits of the UN offices and Peace Institutes and the Economist Intelligence Unit.
In this year, the list has seen the world become less peaceful for the third year in a row - and highlights what it says is a continuing threat of terrorism.
source : http://www.china.org.cn/top10/2011-05/31/content_22683362.htm
Here are the top 10 most peaceful countries as ranked by GPI 2011:
2) New Zealand
5) Czech Republic