You are allowed to stay outside the United States a maximum amount of 12 months with your green card.
If you are planning to stay outside US for more than 12 months, then you must apply for “Travel Document” which allows for leaving USA for up-to 24 months.
You can apply for Travel Document here: I-131, Application for Travel Document
What happens if I stay outside United States for more than 12 months with my green card?
If you stay outside United States for more than 12 months with your green card, then you can risk having your Permanent Residence status canceled, meaning that US government determines that you have abandoned living in the United States and your green card could be revoked (canceled). This will cause significant difficulties in returning back to United States and might require the person to re-apply for immigrant visa again.
If you are a SIV holder and had your green card revoked due to staying more than 12 months outside United States, then this would mean applying for the SIV process all over again with a new application to get another visa re-issued.
Official Source: https://help.cbp.gov/app/answers/detail/a_id/820/~/can-a-u.s.-lawful-permanent-resident-leave-multiple-times-and-return
— ترجمه گوگل —
.شما می توانید تا 12 ماه خارج از ایالات متحده آمریکا با کارت سبز خود بمانید
.اگر قصد دارید در مدت بیش از 12 ماه در خارج از ایالات متحده بمانید، باید برای “تراول داکومنت” درخواست کنید که اجازه می دهد تا ایالات متحده را تا 24 ماه دیگر ترک کنید
I-131, Application for Travel Document :شما می توانید برای تراول داکومنت اینجا را درخواست کنید
چه اتفاقی می افتد اگر بیش از 12 ماه با کارت سبز من در خارج از ایالات متحده اقامت داشته باشم؟
.کارت سبز شما لغو خواهد شد ممکن است لازم باشد مجددا ویزای مهاجر را درخواست کنید.