An integration type A/D converting method includes 11 ) making bidirectional integration to zero voltage V 0 and standard voltage Vb, obtaining count value T0, 12 ) making bidirectional integration to reference voltage V 1 and standard voltage Vb, obtaining count value T1, 13 ) making bidirectional integration to switching voltage Vx and standard voltage Vb, obtaining count value Tx, 14 using formulae Vx = ( V 1- 1- V 0 ) ( Tx - t 0 ) / ( t 1- 1- t 0 ) + V 0 to calculate switching voltage Vx value. Bidirectional integration in Above-mentioned steps includes following steps: 1, to proceed positive direction timing integration to 0 or V 1 or Vx, timing time being the fixed time Td when integrating circuit output voltage passing zero, 2, stopping integration when reaching integration time Td, beginning reversal integration to integrator adopting standard voltage Vb, at the same time counter beginning counting, 3, when integrator output voltage passing zero, generating triggering signal to stop counter counting, respectively obtaining count value T0, T1 or Tx corresponding to voltage V 0, V 1 or Vx. Said invention also discloses A/D converter to realize above-mentioned method.