The principle of using an air ionization chamber to monitor doses in heavy ion radiation research is described. A 239Pu α source was used to measure the saturation curve of the ionization chamber and calculated the collection efficiency. The experimental results showed that the saturation voltage ranged from 50 to 1000V

and a higher collection efficiency was obtained at higher voltage in the saturation area.The method of calculating the collection efficiency is reliable and can be used to correct doses in the experiments with regard to biological effects of heavy ion radiation.