回複：母親有綠卡，回大陸已四年，還可以回美國嗎？

When was the last time your mom left US? If it was over one year ago, your mother needs a travel document issued by USCIS or US Consult to enter US. She can't use her green card under this cirsumstance. If she has not filed 1040 for 4 years, she has abandoned her permanent residency.