As a general rule, you will need to show a passport from your country of citizenship or a refugee travel document to travel to another country. In addition, there may be additional entry/exit requirements in a foreign country (for example, visa).
If you wish to enter the United States after a temporary trip abroad, you will need to present a valid green card that has not expired (Form I-551, Permanent Resident Card). Upon arrival at the port of entry, a U.S. Customs and Border Protection officer will check your green card and any other identification documents you provide, such as your passport, Alien ID, and other identification documents, and determine if you can enter the United States.
Travel-abroad for more than-1 year
If you plan to be absent from the United States for more than a year, it is recommended that you first apply for a reentry permit on Form I-131. Obtaining a re-entry permit prior to leaving the United States allows a permanent or conditional resident to apply to enter the United States during the period of the permit without the need for a visa to return to a US embassy or consulate abroad.
Please note that this does not guarantee entry into the United States upon your return, as you must first be deemed eligible; however, it will help you establish your intention to permanently reside in the United States.
If you remain outside the United States for more than 2 years, the validity of any re-entry permit issued before you left the United States expires.
In this case, it is recommended that you consider applying for Returning Resident SB-1 Visa at your nearest U.S. Embassy or Consulate. The SB-1 applicant will be required to prove eligibility for an immigrant visa and undergo a medical examination. An exception to this process is the spouse or child of a member of the United States Armed Forces or a civilian employee of the United States Government who is abroad on official orders.
In addition, being absent from the United States for six months or more may disrupt the continuous residence required for naturalization. If your absence lasts one year or more and you wish to remain permanently resident in the United States for naturalization purposes, you may file an Application for Retention for the Purposes of Naturalization on Form N-470.