She stared at me with a blank expression on her face.

她木然地盯着我。

《牛津词典》

In it, a mother is asked to interact with her child in a normal way before putting on a blank expression and not giving them any visual social feedback.

实验中，一位母亲被要求以正常的方式与她的孩子互动，然后面无表情，不给他们任何视觉上的社交反馈。

youdao

Emily turned to him with a blank expression.

艾米丽转向他，脸上毫无表情。

youdao

Mr Holmes, who was present for the hearing, sat in red prison dress with a blank expression throughout the proceedings, witnesses said.

BBC: Batman suspect James Holmes 'set booby-traps' in flat

He just looked at me with a blank expression.

FORBES: Adviser Soapbox

However, on television, a blank or flat expression does not look blank.

FORBES: Smile For The Camera -Media Training