The invention discloses a three-dimensional photocatalytic composite fiber material and a preparation method thereof, and belongs to the field of synthesis and application of environmental functional materials. The composite fiber material is the three-dimensional photocatalytic composite fiber material formed by loading Ag3PO4 on MoS2@TiO2 fiber serving as a matrix; the preparation method comprises the following steps: preparing a nano-TiO2 fiber matrix by an electrospinning technology, then synthesizing MoS2@TiO2 heterostructured fiber with vertically distributed monolayer/multilayer MoS2 flakes through a hydrothermal reaction, and finally preparing the three-dimensional composite photocatalytic fiber Ag3PO4/MoS2@TiO2 through chemical deposition. The three-dimensional photocatalytic composite fiber material overcomes the defects that the conventional Ag3PO4 photocatalytic material is slightly soluble in water and poor in depositing performance, solves the problem that Ag3PO4 is easily reduced by photogenerated electrons and thus deactivated in the process of photocatalytic degradation, and can effectively improve the photocatalytic organic pollutant degrading rate under visible light irradiation.