According to X-ray structure analysis, it was found that there exist oxygen disordered defects in the crystal lattice of the samples without exception as x was changed from 0 to 1 in La_(1-x)Sr_xFeO_(3-x). With the doping of Sr~(2+), the crystal lattice was distorted extremely, even the crystal type varied. The results of TG showed a large amount of lattice oxygen released under high temperatures as x>0.5 in the samples. After comparison between the experiment results of the three systems La_(1-x)(Ca, Sr)_xMO_(3+x) (M=Mn, Fe and Co), it was concluded that the occurrence of solid defects is affected by the geometric factor and the catalytic activity is related to the concentration and the ordering extent of oxygen defects. According to X-ray structure analysis, it was found that there exists oxygen disordered defects in the crystal lattice of the samples without exception as x was changed from 0 to 1 in La - (1-x) Sr_xFeO_ (3-x). With the doping of Sr ~ (2+), the crystal lattice was distorted extremely, even the crystal type varied. the results of TG showed a large amount of lattice oxygen released under high temperatures as x> 0.5 in the samples. After comparison between the experiment results of the three systems La_ (1-x) (Ca, Sr) _xMO_ (3 + x) (M = Mn, Fe and Co), it was concluded that the occurrence of solid defects is affected by the geometric factor and the catalytic activity is related to the concentration and the ordering extent of oxygen defects.