The invention provides an oxidizing gas concentration detection method and device. The oxidizing gas concentration detection method and device are suitable for trace oxidizing gas detection. Accordingto the oxidizing gas concentration detection method, a metal oxide in which a nano conductive matter is dispersed is subjected to an electroreduction reaction and a photoreduction reaction; the electroreduction reaction and photoreduction reaction of the metal oxide are stopped, first pulse width modulation signals are applied to the metal oxide, and the reduced state resistance value of the metal oxide is read; an oxidizing gas is supplied to the reduced metal oxide, photocatalysis is performed on the oxidizing gas and the reduced metal oxide, so that the oxidizing gas and the reduced metaloxide can be subjected to a redox reaction; second pulse width modulation signals are applied, the oxidized state resistance value of the metal oxide is read; and the concentration of the oxidizing gas is obtained through conversion calculation based on the ratio of the oxidized state resistance value to the reduced state resistance value.