The invention discloses a floating sediment-boron nitride composite photocatalytic material and a preparation method thereof. The preparation method comprises the following steps: (1) drying and dewatering sediment to obtain a sediment powder material; (2) uniformly mixing urea and boron trioxide according to a mass ratio of 1:2, and performing a high-temperature polycondensation reaction at 1100 DEG C to prepare a boron nitride powder material; and (3) grinding the sediment and the boron nitride according to a mass ratio of 1:(0.3-1), performing uniform mixing, adding water, performing uniform stirring, performing shaping to obtain blocks, and performing calcining at 1000-1500 DEG C to prepare the floating sediment-boron nitride composite material. According to the preparation method, the composite photocatalytic material capable of floating on water is prepared from the sediment and the boron nitride used as raw materials for the first time; sunlight can be fully utilized, and no stirring is needed; and the composite photocatalytic material is especially applicable to the field of sewage treatment.