A method used for preparing fuel oil gas by Dunaliella algae powder relates to fuel oil gas. The present invention provides a method for preparing the fuel oil gas by the Dunaliella algae powder. The marine cultured Dunaliella after harvesting is dried to be made into algae powder; the algae powder is mixed with a solid acid catalyst uniformly and then is processed for the catalysis pyrolysis transformation reaction inside a fluidized bed reactor by N2 as fluidizing gas to obtain the fuel oil gas. Because the Dunaliella is single cell eukaryotic green algae, which has the characteristics of high photosynthesis efficiency, strong environmental adaptability, short growth period, high biological output, not taking farm land, etc., the Dunaliella can grow by concentrated seawater, sunshine, CO2 and little inorganic salt, which has low cost and can be processed for the pyrogenation without pretreatment after harvesting and drying. The solid acid catalyst is used to pyrolyze the Dunaliella as the fuel oil gas under quite low temperature, which can improve the oil gas yield; the oil gas ratio and the product distribution are changed according to different purposes, which is in favor of fitting for the requirements of the fuel oil gas at multiple aspects and has outstanding effect.