妄自菲薄

wàngzìfěibó
  1. to be unduly humble (idiom)
  2. to undervalue oneself

CEDICT

to excessively see oneself as inferior; to look down upon oneself excessively

Wiktionary

過於自卑而不知自重。

重編國語辭典

Entry Composition

1 妄 wàng
  1. absurd
  2. fantastic
  3. presumptuous
  4. rash
2 自 zì
  1. (bound form) self; oneself
  2. from; since
  3. naturally; as a matter of course
3 菲薄 fěibó
  1. humble
  2. meager
  3. thin
  4. to despise