Is it possible for a legal resident of the United States to leave and return to the country multiple times? Yes, but there are risks.
If you are a lawful permanent resident (green card holder), you may leave and return to the United States repeatedly as long as you do not intend to remain outside the country for a year or longer.
If you plan to stay outside the United States for a year or longer, you must apply for re-entry authorization from the United States Citizenship and Immigration Services (USCIS) before leaving the country.
This authorization allows a lawful or conditional permanent resident to apply for entry into the United States upon returning from a foreign country during the period of validity of the authorization without the need to obtain a return visa from a U.S. embassy or consulate.
Re-entry permits are generally valid for two years from the date of issue. Therefore, if you remain outside the United States beyond the date the permit is issued, you may be denied entry into the United States.
To apply for re-entry authorization, you must submit a travel document application (I-131) to USCIS.
If you have applied for permanent resident status but are not yet an official green card holder and need to leave the United States for urgent reasons, you must apply for and receive advance parole to leave the country by filing an I with USCIS Submit -131.
For more information, see the USCIS Policy Manual.
It is mandatory that you provide the required documents before leaving the United States. Otherwise, you may be deemed inadmissible and refused re-entry.
If you are a green card holder and have not been outside the United States for more than a year, you must have either your green card (I-551) or your return visa to re-enter the United States. It is not mandatory to present your unexpired passport; However, it's not a bad idea to take it with you.