An individual may depart the U.S. for a period of six months or less without affecting permanent residence status. However periods of more than six months but less than one year are presumed to break one’s residence, unless evidence is proven otherwise. Departures for more than one break one’s residence and may be deemed a bar to re-entry as a permanent resident. It is a common misconception that merely returning to the U.S. for a short period of time within one year is sufficient to revalidate permanent residence.
You should get a consultation with an immigration attorney prior to going on your trip. You maybe eligible for a reentry permit but most importantly you have to make sure that there is not any reason why you maybe barred from coming back into the U.S. once leaving.