吓得目瞪口呆的；

1. as if struck dumb with astonishment and surprise

    e.g. a circle of policement stood dumbfounded by her denial of having seen the accident
           the flabbergasted aldermen were speechless
           was thunderstruck by the news of his promotion

    Synonym: dumbfoundeddumfoundedflabbergastedstupefiedthunderstruckdumbstruck