The invention relates to a method for preparing a direct reduced iron by a gas base method, in particular to a technology for preparing the direct reduced iron by taking the bio-oil and iron ore powders as raw materials. The method comprises the following steps of firstly sending the bio-oil and water vapor into a water vapor reforming reactor, converting the carbon-hydrogen-oxygen-contained organic matter in the bio-oil into a mixed gas with principle components of hydrogen and carbon dioxide, obtaining a reduced gas with the hydrogen concentration of more than 90vol% by a tail gas purifyingand collecting system, subsequently preheating the reduced gas to the temperature of 100-200 DEG C and sending the preheated gas into a reduction reactor containing the iron ore powders, starting a self-heating system and controlling the temperature in the reduction reactor within 650-900 DEG C and keeping the temperature for 1-2h so that the reduced gas and the ferric oxide in the iron ore generate an oxidation-reduction reaction to obtain the direct reduced iron. The method is characterized in that a coke or a natural gas is not needed and the reproducible bio-oil raw material is used and the method has the advantages of being friendly to environment, simple and quick process, low energy consumption, high metallization rate and high production cost.