Under examination of the effect of oxygen on the lifetime (τ,3,) of ortho-positronium (O-Ps) in perfluorobenzene system, it is found that the effect of oxygen on τ,3, in C,6,F,6, is not marked when Po,2, is less than 9.3×10,3, Pa, but the τ,3, is decreased markedly as Po,2, increases. The experimental results show that the effect of excited molecule ,3,(C,6,F,6,) ,*, on the τ,3, of O-Ps is small.,The kinetic calculation has been performed. The results demonstrate that the following reactions take place in above system:,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42649178&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42649181&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42649179&type=,The values of the original pick-off lifetime(,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42649198&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42649187&type=,http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=42649200&type=,) of O-Ps, K(,3,O,2,+O-Ps), and K(,3,(C,6,F,6,),*, + O-Ps)have been evaluated, 4.15ns, 1.8×10,10,(1•mol,-1,•s,-1,) and 1.7 ×10,10, (1.mol,-1,·s,-1,), respectively.