1. 不易激动的;沉着的;冷静的
If you describe someone as imperturbable, you mean that they remain calm, even in disturbing or dangerous situations.

1. not easily perturbed or excited or upset
marked by extreme calm and composure

e.g. hitherto imperturbable, he now showed signs of alarm
an imperturbable self-possession
unflappable in a crisis

Synonym: unflappable