Imam Mahdi is a divine figure who is on occultation and will reappear at the end times to establish justice in the world. He will establish a just government and will prepare the grounds for man's perfection in all dimensions. There are many traditions (hadith) handed down both by Sunni and Shia scholars regarding his occultation and reappearance. According to many traditions the Imam will reappear at a time when the world is full of oppression and suppression. He will reappear to save the world from oppression and establish justice.
Also there are some traditions on the way of his governance. Some of the features of his government are discussed below.
Salman Farsi quotes the Holy Prophet (PBUH) as saying: "O people! Didn't I preach you for Mahdi?" they replied: "Yes!" He then said: Bear in mind that the Almighty God will rise a righteous and judge man in my Ummah who will establish justice and equity in the entire world at a time when it is overwhelmed with oppression. He is the ninth son of my grandson Hussein (A.S). His name and sobriquet is the same as mine (Nour Software).
Imam Mahdi (AJ) will undoubtedly have a comprehensive plan on his reappearance. His plan will include programs and strategies to eradicate oppression and establish justice and peace. During his rule the people will live in peace and brotherhood.
Imam Mahdi Will Follow Holy Prophet's Method
Commenting on Imam Mahdi's method of governance, Imam Sadiq (A.S) says: "He will act like the Holy Prophet (PBUH) and follows his method. He destroys every oppressive system as the Holy Prophet demolished the foundation of ignorance era and establishes Islam from the very beginning based on the teachings of the Holy Prophet. 
source : www.tebyan.net