I. Introduction
The debt crisis in European area has caused a serious decline of the European economic and threatened global credit market and large banks. It is most severe in five countries: Portugal, Ireland, Italy, Greece and Spain, which are called “PIIGS”. Excessive debts weakened their ability of debt repayment and further financing, which has caused great harm to the European economy. Until now, recession in European area has occurred, and Europe's debt problems gradually dampen the world economic recovery.