A three-component donor-acceptor conjugated polymer (BTNIDNBIBDF-50) film based on dithiophene-aza-isoindigo-bis(2-oxodihydro-7-azaindol-3-ylidene)benzodifurandione was investigated for the sensing characteristics of nitrogen dioxide gas. The effect of semiconductor concentration on the sensitivity of nitrogen dioxide was studied by controlling the morphology of semiconductor film. The polymer semiconductor BTNIDNBIBDF-50 showed the best sensing performance for NO₂ gas at a concentration of 2 mg/mL, and the sensitivity for NO₂ gas at 10×10^-6 (volum fraction) was 121.44%. The experimental results show that bipolar semiconductor polymer BTNIDNBIBDF-50 shows ambipolar charge transport characteristics. Reducing the concentration of the polymer semiconductor will lead to obvious holes on the surface of the film and improve the sensitivity of the sensor to NO₂ gas. However, the excessive porosity can cause the change in gas desorption rate to be greater than the change in adsorption rate, leading to the decrease of sensor sensitivity.