回复：绿卡,我的朋友(18岁)妈妈是美国公民,今年5月他妈妈帮他申

if 他已经拿到了绿卡 (unconditioned GC), which means I-485 approved. The sponsor can not cancel the GC.
But if the I-485 is still pending or the GC he has is with condition, the withdraw by the sponsor can kill his I-485/conditional GC.