Using La(NO₃)₂, MnC₄H₆O₂, citric acid and ethylene glycol (EG), LaMnO₃and LaMn_1-XV_XO₃powers were prepared by Sol-gel with dopant NH₄VO₃. The cayalst were characterized by XRD and used methy orange (MO) as object on photocatalytic oxidation experiment. And effect of heat temperature, cayalyst mass and dopant amount were discussed on degradation rate of MO respectively. The kinetic equations of the process of MO photodegradation were explored. The results show that crystal structure and photocatalytic oxidation degradation rate of MO by LaMnO₃ had been not affect by calcination temperature higher than 700 _oC; the photocatalytic oxidation degradation rate of MO by LaMn_1-XV_XO₃decreased with the increase of the doping amount due to effect of V ion on LaMn_1-XV_XO₃crystal structure; the catalysts were followed first-order kinetic.