The invention relates to the technical field of artificial alga reefs and provides a suspension alga reef structure comprising an alga reef base body and a plurality of auxiliary reef bases. The bottom of the alga reef base body is provided with a plurality of connecting grooves, and metal rods are disposed in the connecting grooves. The lower sides of the connecting grooves are provided with balancing weights which are provided with connecting rings. The side surface of the alga reef base body is provided with connecting holes and the side surfaces of the auxiliary reef bases are provided with connecting pillars; the bottoms of the connecting grooves are provided with pin holes communicated with the connecting holes; the connecting pillars are provided with limiting holes; limiting pins are arranged in the pin holes; the upper ends of the limiting pins penetrate into the limiting holes in the connecting pillars and the lower ends of the limiting pins are connected with the connecting rings. The bottoms of the auxiliary reef bases are connected with the side surface of the alga reef base body through steel cables. The alga reef base body is internally provided with an air storage cavity and the auxiliary reef bases are internally provided with closed cavities. The suspension alga reef structure can protect alga seedlings at the initial stage of delivery and provide wider growth space for algae after the algae are in the mature period, thereby being beneficial to alga multiplication.