How to Maintain Green Card Status
Instructions
1Reside permanently in the United States and limit the length of time you spend outside of the United States. Do not move to another country with the intention of staying and don't leave the United States for more than one year. Either action can result in a determination that you abandoned your green card status. Remaining outside of the country for periods less than a year can also result in abandonment, if an immigration officer determines you did not intend to make the United States your permanent residence.
2
Obtain a re-entry permit before departing if you must leave the country for longer than a year. This permit does not guarantee your re-entry, but it will serve as evidence of your intent to make the United States your permanent residence. If you leave for more than two years, however, you must apply for a returning resident visa at the nearest U.S. Embassy or Consulate. Maintain ties to the United States while you are gone. Examples of this include keeping up a residence and mailing address, place of employment and a bank account, as well as having family here. These connections serve as additional evidence that you intend to permanently reside in the country.
3
File your required income tax returns while outside of the United States. Failure to file your taxes can result in loss of permanent resident---green card---status. Additionally, do not declare yourself a "nonimmigrant" on your tax returns.
4
Abide by all state and federal laws. Violation of the law can result in loss of green card status and deportation. Activities categorized as crimes of moral turpitude, or those resulting in a sentence of one year or longer, can result in loss of status. Deportable crimes include failure to register as a sex offender; drug violations; illegal firearm sales and possession; aggravated felonies; domestic violence; and child abuse.
Source...