Nowadays, people should pay more attention on the environment problems that had advent along with the development of rare earth metallurgy industry. A large number of water pollutant, air pollutant and solid pollutant were discharged in the process of synthesis of rare earth compound by precipitation and roasting process. In order to solve the industry pollution problems, a new technology route was developed for the preparation of lanthanum oxide using lanthanum chloride as raw material by oxy-hydrogen flame route. The experiment results showed that lanthanum chloride could directly convert to lanthanum oxide under high temperature by the combustion of mixture gas of hydrogen-oxygen that provided by oxy-hydrogen generator continuously. The phase composition of obtained product was characterized by XRD and the conversion rate of lanthanum chloride and the reaction mechanism were discussed.