The invention provides a method and a device for simulating the water bloom floatation of blue algae, belonging to the field of water environment. The device comprises a reaction column, a light source and a heating sink, wherein the light source and the heating sink are arranged at the top of the reaction column; the top of the reaction column is sealed aseptically; the outer surface of the reaction column is provided with an aseptic aeration inlet, a culture liquid inlet, an aseptic stirring airflow inlet and a circulating water inlet; the middle of the reaction column is provided with a sampling inlet; and the lower part of the reaction column is provided with a circulating water inlet. The method comprises the following steps: carrying out the amplification culture of algae species; sterilizing culture fluid and a simulating device; placing the culture fluid in the reaction column; inoculating the blue algae into the reaction column for sealing; setting environmental conditions; and then, periodically sampling to analyze and observe the floating characteristics of the blue algae. The method enables the algae to grow in aseptic environments and can effectively simulate the waterbloom of the blue algae. The device has simple structure, small size, easy operation, strong removability, indoor and outdoor use, corollary use with an illumination culture box, convenient manufacture and low cost.