他的表情很严肃。

Tā de biǎoqíng hěn yánsù.

His expression is so serious.

你的表情很有趣哦！

Nǐ de biǎoqíng hěn yǒuqù o!

Your expression is so interesting.

他好像很冷静，没什么表情。

Tā hǎoxiàng hěn lěngjìng, méi shénme biǎoqíng.

He seems so calm and expressionless.