泰然自若

tàiránzìruò
  1. cool and collected (idiom); showing no sign of nerves
  2. perfectly composed

CEDICT

being calm and composed even under the most stubborn and difficult of situations

Wiktionary

形容遇到緊急或危難的情況時，仍能沉著鎮定而不驚惶失措。

重編國語辭典

形容遇到緊急或危難的情況時，仍能沉著鎮定而不驚慌失措

維基詞典

Entry Composition

1 泰然 tàirán
  1. calm
  2. self-composed
2 自若 zìruò
  1. calm
  2. composed
  3. at ease