The invention relates to a method and a device for continually preparing fat alkyl amide propyl amine oxide, and aims to provide a method which has the advantage of simple process route and a device which has the advantage of simple configuration. The method for continually preparing the fat alkyl amide propyl amine oxide includes the steps: 1) leading PKO, hydrogen peroxide and water into a fixed-bed reactor; 2) enabling gas oxidizing agents to enter the fixed-bed reactor, and performing reaction for the PKO, the hydrogen peroxide and the gas oxidizing agents in the fixed-bed reactor under the action of catalysts; 3) separating materials by a gas-liquid separator after the materials are discharged from the gas-liquid separation fixed-bed reactor after reaction is finished. A gas phase serves as the gas oxidizing agents to return to a gas buffer tank and is repeatedly used, and a liquid phase is the amine oxide. The device for continually preparing the fat alkyl amide propyl amine oxide comprises a liquid state material inlet, a static mixer, the fixed-bed reactor, the gas-liquid separator, the gas buffer tank and a fan.